With your Apple Cash, credit, and debit cards stored in the Wallet app on your iPhone, you can use Apple Pay for secure, contactless payments wherever you see contactless payment symbols.
Using Apple Pay With Your iPhone
Using Your Default Card In Your Wallet At The Register:
First, unlock your iPhone with your Face ID, Touch ID or Passcode open Apple Wallet.
Double-click the button on the right side of your iPhone (or tap your home button twice on older iPhones). Or you can hold your iPhone near the contactless reader.
Your default card should appear. Then double tap to authenticate with your face or passcode.
If completed correctly, you should see “Done” and a checkmark appears.
Note: If you want to use a different card you can choose which card you want at the point of payment authentication.