Classes/Structs Question

Hey
I've been a member on this site for quite a while now, but I don't use it nearly as much as I want to (especially considering the brilliant help I've received on here in the past), so here's just a quick question to get me into the flow of using the forums more, and to aid me a bit with my research.

What're the distinct differences between a class and a struct? Is a class just a type of struct or are they two separate objects with different properties?

Thanks in advance
Sam