Can someone explain how a switch works and what are its advantages?

I know that they basically are a communication hub for devices connected via Ethernet cable, but how?

Does the LAN connection being stronger mean that the devices that are connected in that LAN have better and faster internet?

If so do other devices that aren't in that LAN experience an internet speed boost since the other devices don't take up as much internet or are they not interconnected?

EDIT: Also are they as easy to hook up as I think they are? Just plug it in and plug everything else in it and then you're good to go?