the retailers currently use bitpay/coinbase. where you send coins to an address a retailer gives you, which bitpay/coinbase gave them..

in the near future what will happen is that you will put a pocketmoney amount into a bitpay/coinbase account and simply tell the cashier to debit your account for the total. this way the coins are verified (as they have been preconfirmed when u deposited) and is faster then the cashier getting a QR code, printing it, showing it to you and then you fiddling around with your phone to pay them.

this will be done simply by a nfc in your phone coded to you bitpay/coinbase account.

now imagine the speed of your bitcoins paying for your groceries..fully confirmed and no need to press a single button on your phone