Read the links below about various ways to pay for items in the iTunes and App Stores. Apple will automatically try to charge your personal account balance first and then charge any payment methods you have entered such as cards, unless it is something for which you cannot use personal balance to pay for the item.
- Add a payment method such as a credit or debit card to your account. See this link about 'Payment methods that you can use with your Apple ID' --> Payment methods that you can use with your Apple ID - Apple Support then see this link about how to 'Change, add, or remove Apple ID payment methods' --> Add a payment method to your Apple ID - Apple Support
- Add money to your Apple ID balance - "Use a payment method, such as a credit or debit card, to add funds to your Apple ID balance." This takes the previous payment method one step farther by optionally using it to irreversibly add balance to an Apple ID instead of having the card charged each time.
Click here --> Add money to your Apple Account balance - Apple Support
- Create and add money to an iTunes Pass - "At Apple Stores and select retailers, you can add store credit directly to the Apple ID that you use for App Store, iTunes Store, and iBooks Store purchases." - https://support.apple.com/HT203021
- How to redeem your Apple Gift Card or App Store & iTunes gift card --> How to redeem your Apple Gift Card or App Store & iTunes gift card - Apple Support