How does 3 phase power operate single loads?
3-phase can take two forms.  The general high voltage transfer lines are called "3 Phase Delta" configuration.  In this arrangement the power forms a triangle. It's easiest to understand it from the PoV of a transformer's windings:



The other form, which is used for local distribution amongst properties, is called "3 Phase Star".  The triangle is kind of turned inside out and it forms a star:



A normal household would get N and one of L1, L2 or L3 (in the US and some other countries you get "split phase" where one line signal is divided into two).

A special transformer which has both types of winding arrangements in it converts the delta to star format:



The voltage between Lx and N is the normal "line" voltage for your country (240V in the UK, 110V in the US, etc).

The voltage between two Lx lines is the "3 phase" voltage for your country - 415 in the UK, 203V in the US.

So a normal light bulb would be connected between, say, L1 and N.