If you received a game item as a gift, the code is located inside the gift email. Alternately, you can click on the link in the e-mail to claim the game item.
For codes from the World of Warcraft Trading Card Game, or item or pet codes released prior to BlizzCon 2009, use the World of Warcraft code redemption page.
The item will be sent to the in-game mailbox of all eligible characters associated with the destination Battle.net or World of Warcraft account (refer to the item description for details). Make sure the character has inventory space available before taking possession of the item.