Credit cards are different from debit cards because

Debit cards are used to pay for goods in shops and to withdraw money at cash machines. The money is automatically taken from your current account when you spend it, so you must have enough money in your account or an agreed overdraft to cover the transaction.

Where as..
A credit card, such as Barclaycard, isn't linked to your current account and is a credit facility that enables you to buy things immediately, up to a pre-arranged limit, and pay for them at a later date. The cost of the purchase is added to your credit card account and you get a statement every month.