Go to the main iTunes Music Store page (within iTunes), click on the "Redeem" link on the right side of the page, and enter in the code from your card. You'll be able to create an iTunes Music Store account without needing a credit card.
Forum Tip: Since you're new here, you've probably not discovered the Search feature available on every Discussions page, but next time, it might save you time (and everyone else from having to answer the same question multiple times) if you search a couple of ways for a topic, both in the relevant forums, in the
User Tips Library and in the
Apple Knowledge Base before you post a question.
Regards.