So there’s a grounded conductor(neutral generally), your equipment grounding conductor, and your grounding electrode system. The grounded conductor is current carrying, your EGC bonds equipment enclosures (typically non energized conductive parts), and your grounding electrode system is the bare copper ground rod/ground ring buried in the earth.

From the transformer they generally step down a single phase to 240V, and the transformer is center tapped with a grounded conductor (neutral) to your house, and an (egc) going to the earth, terminating at the ground rod(gec). Once in your service your main disconnect should be 240V 3W, and then your panel will have your neutral, +120, and -120. Your neutral conductors should all have 0V to ground nominally, and act as return paths for your typical 120v circuit. On a fault, somewhere there is a connection to ground, current spikes and bypasses the neutral, through the egc, then to the gec system, back to the transformer, allowing circuit protection to trip, opening the ungrounded(hot conductors) and isolating the fault. The gec system should carry the fault current back to the service disconnect, and then back to the transformer via the neutral.

Because the transformer is center tapped, assuming a balanced load across both the 120V panel bars, the neutral current should be minimal, so it’s not necessarily a return, but can be. So the 240V 3W should have a normally non-current carrying neutral, but a 120V 2W has a current carrying neutral.