How to purchase from wallet

To use Apple Pay, first make sure it's set up - Set up Apple Pay - Apple Support

Then, to use it, look for the contactless symbol, which may look like either of the examples below.

If you are at a location that supports Apple Pay, simply double-click the side button quickly to activate it, then use Face ID or enter your password to authenticate it. Hold it near the card reader, and it should work.

Use Apple Pay for contactless payments on iPhone - Apple Support

See instructions in Make purchases using Apple Pay - Apple Support