Different types of keyboard components include the membrane, the PCB, and the switches. 
The membrane is a thin piece of plastic or rubber that covers the keyswitches and connects to the PCB. It's usually made from a soft material so it doesn't make noise when you press down on it. 
The PCB is a large board that houses all of the electronics necessary to control the key switches. It usually has sockets for USB and other connectors, as well as slots for the membrane and other components. 
Switches are tiny pieces of metal that sit on top of each keycap and allow you to type without having to press down on any of the keys. They're activated by pressing down on one end and then pulling up, which pushes a switch inside against the resistance of the spring tension.