Can i use the itunes card to purchase an app?
Yes, iTunes gift cards can be used to purchase apps from the iTunes app store, as well as music, films etc from iTunes, ibooks from the ibookstore, and Mac apps from the Mac App Store.
How should i do it? Since, every time i tried to click the "BUY APP" button, it always asked fir my ccard.
As long as you are buying for yourself, and not gifting content, then your account's balance should automatically be used up first. How purchases are billed : http://support.apple.com/kb/HT5582
Is it a newly created account ? If it is then depending upon how you created it then card details may need to be entered before you will be able to use it to download any item from the store - only if the instructions on this page were followed when creating the account will you be able to use it without first giving card details : http://support.apple.com/kb/HT2534
Can i use the itunes card to purchase an app?
