Unlock your phone as your normally would using your passcode, fingerprint, etc. and hold it near the contactless reader. A subtle vibration and beep will let you know the payment information was successfully sent.

For purchases in Apps and websites that that support Google Pay, simply choose the Google Pay option at checkout and follow the on screen instructions.

Note: For convenience, Google allows for limited transactions to made when your phone is locked. You should therefore secure your phone with the same care you would your cards.