Hi, the Apple Card is a MasterCard and can be used worldwide anywhere MasterCard is accepted. Apple Pay is separate from a credit card and is a payment network. If your friends have a merchant account and they accept MasterCard, you can use your Apple Card to make payments. If they also use Apple Pay, as one of their payment networks, you can request they use your Apple Card using Apple Pay. Here is a support article that covers how to use Apple Pay,
https://support.apple.com/en-us/HT201239
https://support.apple.com/en-us/HT209225
If you use the electronic version of Apple Card on your iPhone or Apple Watch, you’ll earn 2% Daily Cash Back. If you swipe the physical card at a payment terminal, you’ll only earn 1% Daily Cash Back. Here is a support article that discusses Daily Cash Back and Apple Cash.
https://support.apple.com/HT209227
I hope this helps. If you have any additional questions or concerns please post a reply and a community member will respond.