A laptop keyboard has a key matrix, which is a grid of circuits underneath the keys¹. Each circuit is broken at a point below each key¹. There are three separate layers of plastic that work together to detect your key presses. Two of them are covered in electrically conducting metal tracks and there's an insulating layer between them with holes in it. The dots you can see are places where the keys press the two conducting layers together². The keyboard also has alphanumeric keys, shift keys, and function keys³.