The store will collect the money from the company that issue your credit card. At the end of each month, the credit card company will send you the bill. When you pay your credit card bill, you are paying to the credit card company but no the store.
When you sign your $100 credit payment in the store, the store will acturally receive about $97 from the credit card company. $3 will be taken away. At the end of the month, you will receive the $100 bill from credit card company that you need to pay off. If you can not pay in full, you will see some interest charged the next month on top of whatever you owe to the credit card company.