It's just the default.
talks you through making an apple ID without a credit card.
If you've already made one then you need to make sure you sign out of that one and have another e-mail to use since you can't have multiple accounts to one e-mail.
How to Get Apps From the App Store Without a Credit Card
Creating an iTunes Store, App Store, iBookstore, and Mac App Store account without a credit card
If None is not available - On your computer launch iTunes and click "iTunes Store" in the left navigation pane. Click the "down arrow" next to your name at the top right side of the page and click "Account." Enter your username and password and click "View Account" to log into your account information. Next to your Payment Type, click "Edit." Select the "None" button and click "Done." Confirm that your card has been removed by returning to the Apple account information screen. Under Payment Type, it should say that there is no credit card on file.