When your bill arrives, the credit card company will certainly allow you to pay less than the full balance. You only have to make a minimum payment, which seems like a good deal at first glance.
They're going to charge you interest on every cent that you don't pay off, however, and that interest rate is high.
Let's say you get an $800 credit card bill in the mail, and the minimum payment is $28 (interest plus 1% of the balance). If you just make the minimum payment, that leaves $772 on the card. If you have an APR of 30% on the card, you just got dinged with (roughly) $20 in interest. Your balance just went up to $792. Yep, next month you still owe $792, even though you threw $28 at the card.
Not only that, you now have that $792 debt hanging over your head. Add more to it, and the interest will grow, too, month after month. Minimum payments barely even scratch the balance, and that's by design. Credit card issuers make real money off of you continually paying interest. You get nothing out of it, too. All you got was the ability to make an impulsive purchase, one that you're paying off for months or even years, and you're paying a lot more than that initial cost, too.
How bad is it? If you have $800 on a card with a 30% APR and a minimum payment of the interest plus 1% of the balance, it will take you 113 months to pay it off, and you will have paid a total of $1,261.04. Yep, $461 just vanished out of your pocket for nothing.