beware that you're about to enter a realm that is as anal about fluff as some of those bad trekkie fellas you see @ conventions.
http://en.wikipedia.org/wiki/Warhammer_Fantasy_(setting)
That's got a good introduction and overview. I'd only dip in if I were you - the game setting is literally massive.
You've got the following races:
Elves (High Elves, Wood Elves, Dark Elves high elves ponce about cities, wood elves ponce about in the woods and dark elves ponce about stabbing people)
Orcs & Goblins (Fucktons of tribes of the buggers, spread throughout the old world, some live in former Dwarf Cities which is the root of the Orcs & Goblins vs Dwarfs thing)
Dwarfs (couple of mobs of these boys - mainly live close to the mountains where the orcs live. There are chaos dwarves who've fallen to the dark side so to speak - but they're rare)
Empire - based around germany - humans - lots of the fuckers.
Bretonnia - based around the french - humans - lots of the fuckers
Slann - lizard men - live in Lustria (South America - equatorial regions of the warhammer world)
kislevites (Vikings / kossovans) feckers who live in ze north of the warhammer world - humans - lots of the fuckers
Skaven - Ratmen - they live under ground and can pop up everywhere - evil little fuckers they are
Undead (have necromancer, will raise undead) - again - can rise up anywhere and everywhere
Chaos...
Chaos is huge - just about every destruction race has worked with or for chaos over the years. In Warhammer Online they use Tzeentch I think. The main reason for this is that the various chaos followers are as likely to fight each other as anyone else.
Tzeentch (lord of change) is the chaos god of magic.
Nurgle (Pestillence) Chaos god of disease - hates tzeentch and vice versa
Khorne is the chaos god of blood and murder - his followers tend to have fuck all magic but hit like freight trains
Slaanesh - depravity and perversion - fast and sexeh! Hate Khorne and vice versa
The game world is dark. The good guys are zealots, the bad guys are mass-murdering monsters. The whole premise is that good are failing, with every incursion the forces of destruction seem to get stronger and do more damage. If you've read the wheel of time - think the borderlands and the blight for the Chaos Wastes and the regions of the empire that are subsumed.
It's a pretty good setting tbh - it's definitely all about conflict and war and quite armageddon-esque
M