The current virtual world consists of two planets, Azeroth and Draenor (a.k.a Outland). Azeroth consists of two main continents, the Eastern Kingdoms and Kalimdor. Located to the northwest of Kalimdor are the Azuremyst and Bloodmyst Isles, and Teldrassil.

Kalimdor contains the starting areas for the Orc, Troll, and Tauren races of the Horde. The Night Elves and Draenei of the Alliance both begin in areas off the coast of Kalimdor (Teldrassil and Azuremyst and Bloodmyst Isles respectively), but move to the mainland fairly early. The Eastern Kingdoms contain the beginning areas for the Undead and Blood Elves of the Horde, as well as the Humans, Dwarves and Gnomes of the Alliance.

Draenor, added with the release of The Burning Crusade, is only accessible to those who have purchased and activated the expansion pack. It is reached through the Dark Portal in the south of the Eastern Kingdoms or through in-game teleportation. Draenor was the original home of the Orcs and was also inhabited by the Draenei for over 200 years.

The Wrath of the Lich King expansion will add the continent of Northrend in the northern region of Azeroth and will be available exclusively to those players who purchase and activate that expansion pack.

Content borrowed from wikipedia.org