Use of iTunes gift card credit I have a $50 iTunes gift card credit. How can I use it for the App Store? When I try to purchase an app from the App Store, I am asked to enter a credit card number.  Can I transfer the $50 to the App Store account?
I think this will work...

Open iTunes

Just below the volume bar is your Apple ID. 

Click on that and select Redeem. It will prompt for your Gift Card info..

Here's a little pic: