This circuit diagram shows wiring for a 4 way circuit with the power source at the light fixture and the switches following.
A two-wire cable (C2) is run from the light to the first switch (SW1) and a 3-wire cable runs between all the switches. The hot source is connected to the common terminal on the first switch (SW1) and the hot terminal on the light fixture is spliced through all the light fixture to the common terminal of the last switch (SW3).
The travelers run from the first switch (SW1) to one set of terminals on the 4 way (SW2) and from the second set to the travelers on the last 3 way (SW3). The hot to the light is from the common terminal of SW3 (spliced through each switch box).
In this 4 way light circuit the power source is via the first switch (SW1). The hot connects to the common on that switch and the neutral is spliced through all the switch boxes to the neutral terminal of the light. A Three-wire cable runs between all the switches connecting the travelers.
Four-way switches have four terminals. This type of switch works in combination with two three-way switches to control electricity to lights from three (or more) locations. They support hot conductors (traveller wires), which receive and transfer electricity from each of the three-way switches.
You may also be interested to see how a two way switch works
You may also be interested to see how a three way switch works