How does it know when the mouse is moved?

A computer detects mouse movement through a sensor within the mouse, which tracks changes in position. This sensor can be optical, using a light source and camera to detect surface movement, or mechanical, using a ball that rolls as the mouse moves. The mouse sends this positional data to the computer via a wired or wireless connection, allowing the cursor on the screen to respond in real-time to the movement. The operating system interprets this data, enabling user interaction.