The main types of metal are:
Black
Death
Doom
Electronic
Folk/Viking
Gothic
Heavy/Traditional
Orchestral/Symphonic
Power
Progressive
Speed/Thrash
As recognised by
http://metal-archives.com (which is basically the metal bible on the internet) but people often mix these together, or invent totally new ones as they see fit, so a lot of the ones you may hear about are people just being stupid.