>>2953632
Grid power is generated at power plants by generators that spin. Power plants generate using 3-phase because it happens to be very practical and efficient. The 3 phases are best visualized with pic related. Each phase can be thought of as 120 degrees apart on a circle, so 3 * 120 degrees for the full 360 degrees of a circle.

In America, residential households usually only get a single phase of ~240VAC which is split into two with a center-trapped transformer, which means you get two halves at 120VAC.
Commercial buildings and apartments/condos often get 3 phases instead of the split-single phase, so any single phase to neutral has 120VAC, but the voltage between two phases is around 208VAC for the dryer and stove plugs.

Neutral is the return path for electricity for normal operation, so it carries current when the device runs normally.
Ground is the return path for when there's a safety fault, which normally carries no current. Faults are like when a bare wire touches the grounded metal chassis of an appliance, causing a short circuit tripping the breaker. Or a crack forms in a hot tub heater, causing current to flow to ground, which the ground-fault detector sees and then shuts off the circuit.

>>2953725
>the first wire has the highest, the second a bit lower, and the third the lowest
sorry 3phase has nothing to do with this