I want to get a credit card, but am scared. I don't understand the APR stuff. Do I pay interest every month or only if i dont pay it off?

You pay daily. An APR of 20% is per year, but you'll pay 1/365th of that every day, and its calculated daily. To avoid being scared, don't carry a balance on your card. It's a bad deal.

Pay off the bill in full every month before the due date and you do not pay interest. Carrying a balance does NOT build your credit score more quickly as some people think.

If you do not pay in full you pay interest only on the amount outstanding while it remains unpaid.

If you don't understand credit cards, don't get one.

If you always pay off the card every month, then you don't pay interest.

However, if you pay off the card some months, and not others, then you don't pay interest just for the months when you didn't pay off the card. You also pay interest for some of the months that you did pay off the card.

If you do not pay off the bill every month you have to pay rent for the money you still owe. That rent s called "interest".

If you pay your bill off in full every month you do not need to rent any money and pay no interest.

The APR is how much rent you pay for the money you need to borrow.

Only if you don't pay it off.