A mouse is a tool for pointing at things on a computer screen. When you move the mouse on a desk, the cursor (arrow) on screen moves the same way. You can click the left button once to select something, double-click quickly to open files, and right-click to see more options.
Let children practice moving the mouse in different directions and see the cursor follow. Have them click on different objects, then try double-clicking to open a file.
A computer mouse is a translator between your hand and the screen. When you slide the mouse to the right on your desk, the cursor — the small arrow you see on the screen — moves to the right by the same amount. When you slide left, the cursor moves left. The mouse is always watching how far and in which direction it moves, and the computer instantly moves the cursor to match. You can think of the desk as the "real world" and the screen as the "computer world" — the mouse is the bridge between them.
The left button is the main action button. A single click tells the computer "I'm pointing at this thing." You use it to select a file, highlight text, or press a button. A double-click — two quick clicks in a row — tells the computer "I want to open or run this thing." Double-clicking a file's icon opens it; double-clicking a folder shows what's inside. The timing matters: click too slowly and the computer treats it as two separate single-clicks rather than one double-click. With practice, the right rhythm becomes natural.
The right button works differently. Instead of doing an action, it opens a small menu of options related to whatever you clicked on. Right-clicking on a file might show options like "Open," "Copy," "Delete," or "Rename." Right-clicking on an empty area of the desktop shows options for the desktop itself. It is a way of saying "show me what I can do here" rather than immediately doing something. When you are unsure what's possible with something on screen, right-clicking it is always a safe way to explore.
One thing that confuses new users is lifting the mouse. The mouse only tracks movement when it is touching a surface. If you run out of desk space while moving the cursor, you can lift the mouse, reposition it in the middle of your desk, and set it back down — the cursor will stay exactly where it was. The mouse only "knows" it has moved when it is sliding on a surface, not when it is in the air.