vitamin c serum

All I know about vitamin C (apart from it being good for you!) is that it is one of the water soluble ones (along with vitamin B) so that even if you are 12 oranges today, you would still need some vitamin C tomorrow, as it can't be stored in the body.

Vitamins A,D,E & K are fat soluble, so you need them less often, and can actually do harm if you have to much in a short period.

What effect is vitamin C serum supposed to have on your skin, and how is it claimed to work?

I know we need vitamin c everyday, but in a serum it's supposed to be anti-aging as it is an anti-oxidant so helps fight free radicals, I think. I know we can't halt the aging process but as the saying goes every little helps! Just wondered if anyone has tried it before I spend my money.