Go to Wallet and tap the add button. Follow the steps to add a new card including adding the card security code. You may be required to download an app from your bank or card issuer to add a card to your Wallet. Tap Next. Your bank or card issuer will verify your information and decide if you can use your card with Apple Pay. If your bank or issuer needs more information to verify your card, they'll ask you for it. When you have the information, go back to Wallet and tap your card. After your bank or issuer has verified your card, tap Next and you are good to go!