when do I get a bill from the apple pay card and how do I pay it?

There is no such thing as an Apple Pay Card. What card are you referring to? You do not get a bill from Apple Pay. It’s a payment service, not a credit or debit card. Apple Pay uses credit and/or debit cards that you add to your Apple Wallet app on your iPhone.

Apple Pay - Apple

Make purchases using Apple Pay - Apple Support

You can find your Apple Card statement in the Wallet App by following the steps in the link below.

click here ➜ Download or export your Apple Card statements and transactions - Apple Support

Then see the following link to make a payment towards your Apple Card balance.

click here ➜ How to make Apple Card payments - Apple Support