How to set up my credit card for payment
How to activate my iTunes account
iPhone 4s, iOS 8
Question marked as
This document explains how to add a payment method to your Apple ID on a Mac, Apple mobile devices, PC, or online --> Add a payment method to your Apple ID - Apple Support
On an iPhone or iPad:
1. Open the Settings app.
2. Tap your name.
3. Tap Media & Purchases, then tap View Account. You might be asked to sign in with your Apple ID.
4. Tap Manage Payments.
5. Tap Add Payment Method.
6. Enter the payment method details, then tap Done.