Blizzard, the company that produces 'World of Warcraft,' releases patches periodically to fix game issues, tweak game play and add new content. The first time you open the game, it will download the necessary patches to make your game client match the one the rest of the players are using.

The installation process for either game is pretty self-explanatory - you insert the first disc, start the installer and wait for it to prompt you for the next disk. 'The Burning Crusade' and 'Wrath of the Lich King' are basically upgrades to the 'World of Warcraft' client - it adds new maps and information to the game files. The copy of 'World of Warcraft' you buy at the store is the game client. The Burning Crusade is a trademark, and World of Warcraft and Blizzard Entertainment are trademarks or registered trademarks of Blizzard Entertainment, Inc.