If you need 2 switches to control a light then you would use two 3way switches.
If you need three switches to control a light then you would use two 3ways with one 4way.
If you still need more switches just add 4ways. Need six switches? Use two 3ways with four 4ways.
➳ Weather you use one 4 way or more, the 4 way will not work without two 3 ways.
A 4way switch has 2 "IN" terminals and 2 "OUT" terminals. They are identified on the switch with the words "IN" and "OUT" or there might be 2 marks identifying a pair of terminals as either "IN" or "OUT" The 2 traveler wires from one 3way are connected to the 2 "IN" screws or the 2 "OUT" screws but never one traveler to "IN" and the other to "OUT"