I'm not really an expert because I myself have trouble distinguishing the different types.
I know that the main categories are:
Black Metal
Death Metal
Thrash Metal
Doom Metal
I don't really like the vocals of most bands in Death Metal but there are some that are tolerable such as Dimmu Borgir and At The Gates.
Now more instrumental type of stuff is Black Metal. I think. Using Dimmu Borgir as an example again it can be classified as Black Metal as well.
Thrash Metal is something like Slayer with really driving fast rythyms.
Doom Metal is really sorrowful and makes you feel emotions. A good example is My Dying Bride and Dargaard(No guitars but ambiance type music made by a metal guy)
Well I hope someone with more knowledge comes here to clear some things up, because when I asked one of my hardcore metal friends she said it was hard to explain as well.
