A computer mouse is an input device that allows you to move a cursor or pointer on the computer screen. It typically consists of a plastic or metal shell that houses a ball or optical sensor that detects movement, two or more buttons that you can click to perform various functions, and a scroll wheel that allows you to scroll through documents or web pages.

When you move the mouse, the ball or optical sensor detects the movement and sends information to the computer, which then moves the cursor on the screen in the corresponding direction. The buttons on the mouse are used to perform various functions such as selecting an item, opening a menu, or executing a command. The scroll wheel can be used to scroll up or down on web pages or documents.