Sorry if this has been done before, but please don't flame me. I've never really understood what the difference between all these metal sub-genres are, can anyone explain what makes music a particular sub-genra like:
Death metal
Technical Death metal
Melodic Death metal
Melodic Black metal
Black metal
Progressive metal
Thrash metal
Doom metal
Gothic metal
Power metal
Groove metal
80's hair metal
Heavy metal
Folk metal
and just metal

Well you obviously haven't heard enough to understand it LOL.

Seriously, the best way to find out is to listen to them. It might take a while, but its alot more effective than trying to read about them.
indeed. Probably check out a little bit from every genre to see the difference. Head to the recommendation thread, it has a lot of bands covered. Metal, due to its diversity, may take a while to soak in, but for a general reference it will probably be enough. Just keep in mind that your initial references will be quite general, as every sub-genre has enough diversity in it as well. Wikipedia is also a help, even though it's not always accurate.

Edit: even though there are people who are very cynical of free downloads, because it's not tr00 enough, it's probably the safest, quickest and cheapest way to sift through the countless bands on offer

“Who are you then?.."
"- I am part of that power which eternally wills evil and eternally works good.”
Yeah I would actually try and list what I know but it would be some what difficult . And yes I agree it takes a bit to soak in the whole genre of Metal not to mention trying to get all the feel and message from all of the sub genres, and maybe looking at the rec thread @ the top and just downloading a song from each genre from a couple bands might help until you can go and get some CDs.