i dont have a credit card

Unless you follow the instructions on this page when creating a new account : http://support.apple.com/kb/HT2534

then credit card details will need to be entered before the account can be used to download any item from the store. If you don't have a credit card then create a new account, and use those instructions - if you want to use the same email account then you will need to replace it on your existing account first e.g. by tappin on it in Settings > iTunes & App Store on your phone, the Store > View Account mnu option on your computer's iTunes or via http://appleid.apple.com