[Haskell-beginners] Difference between types and values

Dear All, I am sure this is a common mistake, and I am happy to be pointed elsewhere for reading. I have spent the last couple of days on the Haskell irc channel, which was very helpful. However, one of the points of discussion left me confused. When we have a type, T, with constructors A and B (e.g. data T = A x y z | B x y) How do I understand the relationship between A, B and T? I had thought I could use the sub-class relationship, but that doesn't seem to be true. Any other pointers very welcome. Matt