Make sure your debit/credit card is activated in the Wallet app.
1. Initiate the Wallet app and then select the card you're going to pay with.
2. Hold the iPhone near the store's card reader.
3. Place your finger on the home button and wait for it to confirm your fingerprint.
4. On the screen, you should see the word,
"Done" as well as feel a vibration when the sale is complete.
4. Remove your finger from the home button.
5. Put your iPhone away, take your receipt from the cashier, gather your purchased items, say a few pleasantries to the cashier then exit the store with your belongings.