the easiest way to tell, is the shunt trip breaker will actually take up 4 spaces in your panel. the 4th space will have a neutral wire coming out of it, along with a lug for power INPUT. when voltage is applied to the shunt trip, it will cause the other 3 poles to open by tripping the breaker.
Phases in AC refer to the number of sine waves of alternating current used to generate the average voltage. In 2 phase, two opposing sine waves are overlapped to give the average voltage delivered, eg 240V in household supplies. In 3 phase, three sine waves are overlapped to produce a more consistent average voltage.
A NEMA 14-30P is a plug. A 14-30R is a 3pole 4wire grounding receptacle for 125/250 volts. To wire the receptacle connect a three wire cable's red and black wires to terminals X and Y respectively. Connect the cable's white wire to the W terminal and the ground wire to the G terminal.