How do I pay in-stores with Google Pay on my Android phone?
Step 1: Wake up & unlock your phone
Wake up and unlock your Android phone. You do not need to open the Google Wallet™ app.
Tip: In most countries, smaller transactions don’t require you to unlock your phone.
Step 2: Hold the back of your phone close to the contactless payment reader for a few seconds
When you’re done paying, a blue check mark will appear on the screen.
Step 3: If prompted, follow the instructions on the screen.
Some stores use older software that asks for a PIN or signature. If you’re asked, follow the steps on the screen.
For more details, go to Tap to pay with your phone – Google Wallet Help