about electrical basic

Electricity will only flow when a voltage difference exists. In a single-phase circuit, the neutral is the electrical path to that voltage difference. In a 3-phase circuit, a voltage difference always exists between each phase, so no separate path is required.

Neutral will be there at source. The Neutral is Grounded to Zero Volt Earth at source - only to avoid high volage biuldup/spark/arc/flashover.

Actual energy flow is between the 3 phases-- a poetic -symmetry!

Marvel at the Genius that concepted 3 phase Electric Generation/Transmission/use.

Now giant Rockets too go 3 phase for perfect and easiest control of trajectory.

Not quite. Consider a step down transformer bank made of three single phase transformers. If the bank is connected delta on the secondary, meant to supply only phase to phase loads, no neutral will be present.

As to grounding... such a bank maybe corner grounded or not grounded at all, in which case, ground fault indication is required by code in many jurisdictions.