How do hybrids work?

[slf2012]

All this talk of hybrid vehicles has left me wondering how they work.

I read somewhere that the conventional engine drives a generator which provides additional power for the batteries, and the electric motor does all the driving, but I can't see that being the case with cars like La Ferrari or the McLaren P1.

Presumably in these cases the conventional engine still has a direct mechanical connection to the rear wheels through gearbox and driveshafts. So how does the electric power get applied?

I don't see how an electric motor can operate independently of the conventional engine and still drive the same mechanical components, so I'm presuming that the motor powers the mechanical components by magnetic field?

Would very much appreciate if someone could explain it to me.