How to add indian debit card.

You might not be able to use that debit card, not all are still be accepted by iTunes. Do you have another card that you could try, preferably a credit card ?

For a card to have a chance of being accepted it needs to be registered to 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 are (and therefore the country which is on your iTunes account).