The way it works here is you can use a normal bank card to pay directly of your checkings account balance, meaning if you have insufficient funds, the card gets declined. A credit (debit) card allows you to pay regardless of you checkings balance. But at the end of the month your negative credit balance must be covered by your checkings account. If it doesn’t cover the whole sum, the debt interest kicks in. A true credit card is essentially the same, but instead of automatically balancing the credit, you have to manually transfer the money to the bank. The advantage being that you can use 2 different banks for credit and checking accounts.