We all have been using mouse, computer one not a rat. Basically in older days, we used to have a ball beneath it which helps tracking the motion of the mouse. But nowadays everything has advanced and we started using a different technology, which is more accurate and easy to use too. Optical Mice have a light(usually red in color) and a camera which clicks thousands of photos per second and send to computer,then computer analyses them and the cursor on screen starts moving. Laser Mice also have the same working just they use infrared light, instead on a red LED.