If i order a psn card and it arrives but i am using a gift card can i still use it or how would it work need aomeone to explain it to me

If there is a number on the gift card like a credit card I think you would just type it in like a credit card, if you're ordering online. If there isn't a number then you would have to go to the store in order to use the gift card.

But how do i pay with the gift card

If you paid for the psn card it'll work they don't care as long as they get the money