Computer essentials

Before you write a web page or a line of Python, you need to be comfortable with the machine itself: where your files are, how to move around quickly, which symbols are which on the keyboard, and what actually happens when you open a website. None of this is difficult, but people who skip it spend years losing files and hunting for keys. This chapter gives you the foundation every later chapter stands on.

By the end of this chapter you will be able to:

• name the main parts of a computer and say what each one does;
• organise your work in folders and always know where a file was saved;
• read a file path and a file extension, and know why they matter;
• use the keyboard shortcuts that save the most time;
• find and name every symbol a programmer types;
• explain in plain words how a web page travels from a server to your screen;
• set up the folder for the project you will build through this book.

1.1 What is inside a computer

Every computer — a laptop, a desktop in the school office, or the phone in your pocket — is made of two things. Hardware is the part you can touch: the screen, the keyboard, the chips inside. Software is the set of instructions that tells the hardware what to do: Windows, Android, Microsoft Word, WhatsApp, and the programs you will write in this book.

The table shows the hardware parts that matter most when you choose, use or repair a computer.

A useful way to remember the difference between memory and storage: memory is your desk, storage is your cupboard. You take a file out of the cupboard and put it on the desk to work on it. The desk is fast but small, and it is cleared every evening. Anything you want to keep must go back into the cupboard — which is exactly what Save does.

The operating system

The operating system is the software that runs everything else. It starts the computer, manages files, and lets programs share the screen, the keyboard and the internet connection. Most computers in Tanzanian schools and offices run Windows; most phones run Android. Many servers on the internet — including the ones that will host your web pages — run Linux. The ideas in this book work on all of them, and where the steps differ we show the Windows way first.

1.2 Files and folders

A file is one saved piece of work: a letter, a photo, a spreadsheet of marks, a page of code. A folder is a container that holds files and other folders. Good folders are the difference between finding last term’s marks in ten seconds and never finding them at all.

Organise by purpose, not by date

Decide on a small number of top-level folders and keep to them. A teacher’s Documents folder might look like this:

Documents
├── School
│   ├── 2026
│   │   ├── Form 2 Biology
│   │   │   ├── Schemes of work
│   │   │   ├── Tests
│   │   │   └── Marks
│   │   └── Form 4 Biology
│   └── Staff meetings
├── Personal
└── Projects
    └── results-system

Each folder answers one question: which year? which class? what kind of document? When you save a file, you already know where it belongs.

Naming files well

A good file name tells you what is inside without opening it.

For anything you will use on the web or in code — and that is most of this book — follow three rules: use lowercase letters, use hyphens instead of spaces, and avoid symbols such as #, &, ? and %. A space in a web address becomes %20, and a # or ? changes the meaning of the address completely.

File extensions

The letters after the last dot in a file name are its extension. The extension tells the computer which program should open the file.

Windows hides extensions by default, which causes two problems. You cannot tell results.html from results.html.txt, so a web page you wrote in Notepad refuses to open in the browser. And a harmful program called photo.jpg.exe appears on screen as photo.jpg. Turn extensions on now; you will need them for every chapter that follows.

Paths

Every file has an address called its path: the drive, then each folder in turn, then the file name. On Windows the parts are separated by a backslash \:

C:\Users\Amina\Documents\School\2026\Form 2 Biology\Marks\term-1.xlsx

Read it from left to right: drive C:, then the folder Users, then Amina, and so on, down to the file term-1.xlsx. Web addresses and Linux computers use a forward slash / instead, and so does most code — even on Windows:

https://example.com/school/2026/results.html

You can copy the full path of any file in File Explorer: hold Shift, right-click the file and choose Copy as path.

Where did it save?

The most common computer problem is not a virus — it is a file saved “somewhere”. Three habits prevent it:

1. Read the Save dialog before you click Save. The box at the top shows which folder you are in. Change it if it is wrong.
2. Check Downloads. Files from the internet, email and WhatsApp Web go to the Downloads folder unless you choose otherwise. Move them to the right folder the same day.
3. Use search. Press the Windows key and start typing part of the file name. In File Explorer, the search box at the top right searches the folder you are in and everything inside it.

1.3 Keyboard shortcuts

A shortcut is a combination of keys that does a job without the mouse. You hold the first key — usually Ctrl — and tap the second. People who use shortcuts are not showing off; they are simply faster, and their hands stay on the keyboard while they type code.

You do not need to learn every shortcut at once. Learn the first table this week, and add a few from the others each week.

The ones you will use every day

These work in almost every program on Windows: Word, Excel, browsers and code editors.

On a Mac, use the Cmd key wherever these tables say Ctrl.

Moving around Windows

In the browser

When editing text

1.4 The symbols programmers type

Code uses symbols that you rarely type in an ordinary letter. Many beginners lose time searching the keyboard for them, or mix up two that look alike. Learn their names: when someone says “put it in curly braces”, you should know at once which keys to press.

The table is for the standard US keyboard layout, which almost every computer sold in Tanzania uses.

Pairs that are easy to confuse

• / and \. The forward slash leans forward like a runner; the backslash leans back. Web addresses only ever use /.
• = and ==. One equals sign puts a value into a name. Two compare two values. Mixing them up is one of the most common beginner mistakes in every language.
• 0 and O, 1 and l. The digit zero and the capital letter O look alike in many fonts, as do the digit one and a lowercase L. Code editors use fonts that make them different — look closely when you copy code.
• Straight and curly quotes. Word processors change " into “ and ” as you type. Code needs the straight ones. If you copy code from a Word document or a PDF and it fails for no reason, the quotes are the first thing to check.

1.5 Typing well

You will type a lot of code. If you look at the keyboard for every letter, each line takes three times as long and you make more mistakes. Ten minutes of touch-typing practice a day for a month is one of the best investments a new programmer can make.

• Rest your fingers on the home row: left hand on A S D F, right hand on J K L ;. The small bumps on F and J let you find them without looking.
• Each finger is responsible for the keys above and below its home key.
• Use free practice websites such as typing.com or keybr.com. Aim for accuracy first; speed follows.
• Learn where the programmer’s symbols are from the table above, and practise typing lines of real code, not just sentences.

1.6 How the internet works

You use the internet every day, but programmers need to know what happens underneath. When you understand the journey of a web page, error messages stop being mysterious, and Chapters 2 to 4 make much more sense.

Clients and servers

The internet is a huge network of computers connected to each other. Most of them play one of two roles:

• A client asks for something. Your browser — Chrome, Edge, Firefox, Safari — is a client.
• A server answers. It is a computer, usually in a data centre, that stores websites and sends them to anyone who asks.

Every time you open a page, your browser sends a request to a server, and the server sends back a response: the page itself, its pictures, its styles and its scripts.

Addresses: IP addresses and domain names

Every device on the internet has a number called an IP address, such as 203.0.113.10. Numbers like that are hard to remember, so we give servers names instead: example.com, necta.go.tz, wikipedia.org. These names are domain names.

When you type a domain name, your device first asks a DNS server — the internet’s phone book — which IP address belongs to that name. Only then does your browser contact the right server. If DNS fails, you see an error such as “This site can’t be reached” even though your internet connection is working.

The parts of a web address

A web address is called a URL. Each part has a job.

https://shule.example.co.tz/results/form-4?year=2026#mathematics

Chapter 7 shows how attackers abuse these parts to make fake addresses look real. The rule from that chapter is worth repeating here: the domain is the part just before the first single /, read from the right-hand end.

HTTP and HTTPS

The language browsers and servers use to talk to each other is HTTP. HTTPS is the same language inside an encrypted connection, so that no one in between — on the café Wi-Fi, or at your internet provider — can read or change what you send and receive. Every website that asks for a password or a payment must use HTTPS, and today almost all websites do.

What the server answers

Every response starts with a three-digit status code that says how the request went. You will see these often once you build your own sites.

Codes that start with 4 mean the request had a problem; codes that start with 5 mean the server had a problem. When you build pages in Chapter 2 and see a 404, check the spelling of the file name and the folder it is in.

The journey of one page

Put together, opening https://example.com/results.html goes like this:

1. You type the address and press Enter.
2. Your device asks DNS for the IP address of example.com.
3. Your browser opens a secure connection to that server.
4. It sends a request: “Please send me /results.html.”
5. The server finds the file and replies 200 OK with the HTML.
6. The browser reads the HTML, sees that the page also needs a stylesheet, some images and a script, and requests each of them the same way.
7. It draws the finished page on your screen.

All of this usually takes less than a second. In Chapter 2 you will write the HTML from step 5 yourself.

1.7 Data: bytes, bundles and saving

Everything a computer stores or sends is measured in bytes. One byte holds about one letter of text. Larger amounts use the units in the table; each is about a thousand times the one before.

You will sometimes see 1,024 used instead of 1,000. Both are in use; the difference does not matter for everyday decisions.

The same units explain your data bundle. Pages that are mostly text cost very little. Video and automatic updates are what empty a bundle quickly. To make a bundle last:

• download large files and updates on Wi-Fi when you can;
• in your phone’s settings, set app updates to install on Wi-Fi only;
• lower the video quality in YouTube and similar apps;
• watch for apps that use data in the background — Android shows data use per app under Settings → Network → Data usage (the exact names differ between phones).

1.8 Set up your project folder

Throughout this book you will build one project, step by step: a small school results system that stores students, subjects and marks, works out grades and divisions, and shows the results on a web page. Each chapter adds a piece.

Create its folder now, so that every file has a home from the first day:

1. Open File Explorer (Windows + E) and go to Documents.
2. Create a folder called Projects if you do not have one: right-click an empty area, choose New → Folder, type the name and press Enter.
3. Inside Projects, create a folder called results-system — lowercase, with a hyphen, no spaces.
4. Inside results-system, create these folders:

results-system
├── web        (Chapters 2 and 3: HTML, CSS and JavaScript)
├── database   (Chapter 4: SQL)
├── python     (Chapter 5)
└── cpp        (Chapter 6)

5. Click once in the address bar at the top of the results-system window to see its full path, and write it down. You will need it when you open the project in your code editor.

In Chapter 8 you will put this whole folder under version control with Git, so that every change is saved and nothing you build can be lost.

Key terms

Check your understanding

1. You were typing a report when the power went off, and the changes are gone. Using the “desk and cupboard” idea, explain what happened and how to prevent it.
2. A student says their web page index.html will not open in the browser, and Notepad shows it was saved as a text file. What is the most likely problem, and what setting would have made it obvious?
3. Write a better name for a file called Copy of marks NEW (2).xlsx that holds Form 3 Chemistry marks for Term 2 of 2026.
4. What is the difference between total = 50 and total == 50?
5. Name the symbols { }, [ ] and \, and give one place each is used.
6. In https://maktaba.example.ac.tz/books?subject=history#top, which part is the domain, which is the path, and which is the query?
7. You open a page and see 404. Is the problem more likely with the address you typed or with the server? What about 500?
8. Why does watching videos use far more of a data bundle than reading news websites?

Answers

1. Unsaved changes are kept only in memory — the “desk” — which is cleared when the power goes off. Only what was saved to storage — the “cupboard” — survives. Press Ctrl + S often.
2. It was probably saved as index.html.txt. Turning on File name extensions in File Explorer would have shown the hidden .txt. In Notepad, choose Save as type: All files and type the full name index.html.
3. For example, form-3-chemistry-marks-term-2-2026.xlsx.
4. total = 50 puts the value 50 into total. total == 50 asks whether total is equal to 50, and gives true or false.
5. { } are curly braces, used for CSS rules and code blocks in JavaScript and C++. [ ] are square brackets, used for lists in Python and JavaScript. \ is a backslash, used in Windows paths.
6. The domain is example.ac.tz (with maktaba as its subdomain), the path is /books, and the query is ?subject=history. #top is the fragment.
7. A 404 usually means the address is wrong or the page no longer exists. A 500 means something went wrong on the server.
8. Video sends many pictures every second, which adds up to hundreds of megabytes an hour. A news page is mostly text, which is very small.