Hi Angela,
The main difference is that the Caravan Club just caters for caravans, while the Camping and Caravanning Club caters for tents etc as well.
They both offer small, five 'van sites (Certificated Sites in the C&CC, Certified Locations in the CC) but, whilst the Caravan Club CLs are limited to 5 caravans, the Camping and Caravanning Club CSs are limited to 5 caravans and as many tents as they can fit in - which puts me off!
I find the C&CC website more helpful, but haven't stayed at any of their sites yet (also new to caravanning).
To be honest, we joined both! This gives us the best choice of sites when we go away.
I think if I was just going to join one, it would probably be the Caravan club - but I think it's worth the extra