Questions about PVP and Battlegrounds...Follow

There are three Battlegrounds (short: BG).

Warsong Gulch (short: WSG) is capture the flag type. You can do WSG from lvl 10 on. It's 10 vs 10.
Arathi Basin (AB) is taking control of bases and holding them to gain resources, racing the opposition to 2000 resources. You can do AB from lvl 20 and on. It's 15 vs 15.
Alterac Valley (AV) is a grand scale multiple objectives based battleground, where the main objective is to kill the opposition's general. It's 40 vs 40.

To join Battlegrounds you have to join a queue and when you are ready to go in you will get a message and can click it to be teleported to the BG area. Queueing for BG is done with the respective Battlemaster which can be found in every major city. With each BG there comes a respective faction for both the Horde and the Alliance. For example, the Horde WSG faction is called "Warsong Outriders" and the Alliance faction for that particular BG is called "Silverwing Sentinels". Each of those factions also has a base of operations where you can get quests, join the queue, and check out what rewards are available. For example if you would like to check out Alterac Valley (highly recommended) it is a good idea to take a flight to Hillsbrad Foothills and find the base of your AV faction. (Stormpike for Alliance, Frostwolf for Horde). They are both in the North on the Alterac border.

Go to http://www.wow-europe.com/en/info/basics/battlegrounds/index.html to read more.
FYI "Eye of the Storm" is a new BG that's coming with the expansion and hasn't been implemented yet into the live game, it might be confusing to see it listed.

Edited, Dec 23rd 2006 4:16pm by Shmii

Minor correction here: the new BG is called "EYE of the storm". "Before the storm" is the name of the 2.0 content update.