How do I use my Apple Card to pay someone

Apple Card is a Mastercard credit card. You can use it to pay businesses or individuals that accept credit cards (including via Apple Pay) but not to pay most people.

You can use Apple Cash to pay someone (but it is advisable to do that only with someone you know and trust). You can fund Apple Cash with a debit card or with some prepaid cards. See: Send and receive money with Apple Cash - Apple Support