text: None.  APR is the annual percentage rate.  It is the interest that you will be paying if you keep a balance on your account.  The more you owe on the card, the more your monthly payment is going to be.  Yes, you agree to pay them back.  If you break it, it will affect your credit history and you will have to pay higher interest when you buy a car or home.  You see the commercial for 0% car loans, they are for almost perfect credit individuals.  If you have bad credit, you could be paying 29% or more.