First, look for the contactless symbol 
at the checkout everywhere Mastercard® is accepted. When prompted for payment, simply unlock your smartphone and hold it near the terminal to make your purchase.
Tips:
- Make sure you are within a few centimeters of the contactless reader to ensure it can properly pick up your card.
- Make sure Stocard is set as the default payment app on your smartphone. Learn how to do it here:
How do I set Stocard as the default payment app on an Android phone?