Unless the instructions on this page are followed when creating an 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.
You could see if this post by mountaingoatgirl lets you review your account without needing to enter credit card details : https://discussions.apple.com/thread/5295285?answerId=24303054022#24303054022
If not then you will need to create a new account, and this time use the instructions on that HT2534 page when creating it. If you want to use the same email address then you will need to replace it on that account first e.g. by tapping on it in Settings > iTunes & App Store on your iPod, via the Store > View Account menu option on your computer's iTunes or via http://appleid.apple.com
Creating an account with 'none' :
computer's iTunes : https://discussions.apple.com/thread/5729572?answerId=24321860022#24321860022
iOS device : https://discussions.apple.com/thread/5847690?answerId=24700173022#24700173022