Debit cards allow you to spend only what is in your bank account. It is a quick transaction between the merchant and your personal bank account. Credit cards are revolving lines of credit made available to you just like a loan. The amount the credit card issuer allows you to use is determined by your credit history, income, debts, and ability to pay. You may use the line available on the credit card with the understanding that you will repay the amount, plus interest if you do not pay in full each month.