"To get started, you can add the credit or debit card from your iTunes account to Passbook by simply entering the card security code.
To add a new card on iPhone, use your iSight camera to instantly capture your card information. Or simply type it in manually. The first card you add automatically becomes your default payment card, but you can go to Passbook anytime to pay with a different card or select a new default in Settings."
Hope that helps. I think ApplePay will benefit Apple not only by creating revenue, but by improving Apple's margins in its own transactions: Apple will be able to act as its own transactions processor at its own stores in all the transactions it previously paid transactions processors to process. http://seekingalpha.com/article/2465365-apples-position-supports-payment-processing-enterprise