What Is a Computer? The Screen, Mouse, and Keyboard Explained

Computer basics, in plain English · Updated October 1, 2026

You do not need to know technical words to start using a computer. Let’s begin with the parts you can see and what each one does.

The four parts of a typical desktop setup

1. The computer: the part doing the work

A desktop computer can be a tall box, a small box on the desk, or a little box mounted behind the screen. People often call a tall one a tower.

Inside are the parts that run your programs and hold your saved files. A program, also called an app, is a tool you use on the computer—for example, a tool for writing a letter.

2. The monitor: the screen you look at

A separate monitor displays what the computer sends to it. Think of it as a window into what is happening.

Turning off a separate monitor usually turns off the screen only. The computer may still be running. When you want to shut down the computer, use its on-screen Shut down option.

There is an exception: an all-in-one computer has its computer parts built into the screen’s housing. We’ll explain that below.

3. The mouse: point, click, and scroll

Move the mouse across the desk and a small arrow usually moves across the screen. That arrow is called the pointer.

• Click: Point at something and press the main mouse button once. This can select an item or press an on-screen button.
• Double-click: Press the main button twice quickly. Many desktop items, such as folders, open this way.
• Scroll: Roll the wheel to move up or down a page.
• Right-click: Press the other button to see extra choices for an item.

Most mice use the left button as the main button, but you can change that in settings. Web links usually need just one click.

4. The keyboard: type words and numbers

Click in the place where you want to write, then use the keyboard.

• Space bar: Adds a space between words.
• Backspace: Usually removes the character just before the typing position. On a Mac, this key is often labeled Delete.
• Enter or Return: Can start a new line, confirm a choice, or submit something. What it does depends on the app.
• Shift: Hold it while pressing a letter to type a capital letter.

You do not need to memorize every key. Start with the ones you use.

How the parts work together

Imagine writing a shopping list:

1. You use the mouse to open a writing app.
2. You use the keyboard to type “milk.”
3. The computer handles your typing and runs the app.
4. The monitor shows the word “milk.”

When you save the list, the computer stores it in the place you choose. Some apps also save files through an online service.

What about laptops and all-in-one computers?

A laptop puts the computer, screen, and keyboard into one device you can fold and carry. The flat touchpad below the keyboard does the mouse’s job: move a finger on it to move the pointer. You can also connect a separate mouse.

An all-in-one looks like a monitor, but the computer is built into the same housing. It usually uses a separate keyboard and mouse. The screen and computer share one unit.

Do I need the internet to use a computer?

Not for everything. Many computers can let you write or view files saved on them without an internet connection. Visiting websites and using most online services needs a connection.

A good first step: Look at your own setup and find the screen, keyboard, and mouse or touchpad. Then see whether the computer is a separate box or built into the device. You have already learned the main parts.

Next steps: What Is a Web Browser? · What Are Files and Folders?

Keep learning: More plain-English tech explanations · Help with an everyday tech problem