You don't have to have a credit/debit card but it is normally used at some point to validate your address so that, for example, you don't try to access the store of a different country.
There are some hoops you can jump through as you create your iTunesaccount that workaround the need for a card, otherwise once the account is set up iTunes may still expect you to provide one, which you can subsequently remove. If you don't have or want to use a credit card at this time you can try this method...
- Enable the menu bar if needed with Ctrl+B (Applies to Windows only)
- Sign out of the iTunes Store from the Store item on the menu bar
- Go to iTunes Store home page
- Go to Quick Links > Redeem
- Sign in with your Apple ID
- Go through the screens, accepting the EULA, etc. You should arrive at a Review Payment screen where one of the options is None - select this and continue... you shouldn't actually need to redeem a new voucher/card
tt2