When you get a credit card, you will have a preset limit on how much you can charge to it. Once you reach this limit, you will not be able to charge any more until you make a payment. After you make a purchase, your available credit will decrease by the amount spent. There will be a period of time, called the grace period, when you can pay it off in full without incurring an additional charge. If you don’t pay off a charge by the due date, you can be charged interest. The amount varies depending on your card’s annual percentage rate (APR). The best practice is to only make purchases with your credit card that you can afford and to pay off your balance in full by the end of the month.