A computer mouse translates planar two-dimensional movements on an outside surface into electrical signals that are then interpreted by a computer so as to move a visual pointer on a graphical user interface (GUI).  Initially, mice utilized a mechanical ball to interpret movement, but most modern mice incorporate an LED or laser to detect the same movement, known as an optical mouse.

Optical mice operate by sensing a small region beneath the device, which is lighted by an LED or laser.  This region sensing is continuously refreshed many hundreds of times per second to ensure any change will be detected quickly and without lag.  Circuitry within the mouse can detect small offsets on the surface when it is moved in any direction.  These changes are translated into signals and sent to the connecting device.  Optical mice can function on nearly any opaque surface, but often have difficulty on glass or reflective material.

Mice also have other functions, typically having one to three buttons that perform various tasks depending on the device that is being interfaced.  Most typically they are used as a selector when the pointer is over a desired location.