I'd be very grateful if someone could spare me a few minutes and give me a brief explanation of the above.

I understand Меня in sentences such as : Меня зовут

But i'm less sure (haven't got a bloody clue) in sentences like : у меня / у него / у вас

I can work out why words like него/неё are used but not the 'у'.

I'd also like to know if the following is correct:

у нас - talking to a single person.
у вас - talking to more than one person.

Apologies in advance if this requires more than a basic explanation as i'm always conscious of taking up too much of peoples time.

Any help would be greatly appreciated.