Q: How do I purchase with my Debit Card?

Whether anybody on here can help you use your debit card depends upon what happens when you try to use it and what country that you are in - from this page :

You may be able to use other payment types in your country, like debit and Maestro cards.

which implies that debit cards are not accepted in all countries, and there have been a number of posts about them being declined.

If your card is being declined, then for a card to have a chance of being accepted it needs to be registered to exactly the same name and address (including format and spacing etc) that you have on your iTunes account, and have been issued by a bank in the country where you and your iTunes account are. If it is then you could check with the card issuer to see if it's them that are declining it, and if not then try contacting iTunes Support (these are user-to-user forums) and see if they know why it's being declined (but you might not be able to use a debit card) : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Account Management

If you are being prompted to review your account then you could see if this post by mountaingoatgirl lets you do so without needing to enter card details : https://discussions.apple.com/message/24303054

Or there are instructions on this page for creating a new account without needing to enter payment details (i.e. you will be able to download free items) : http://support.apple.com/kb/HT2534