When you turn 18, you can apply for another sort of debt – a credit card. A credit card means you're effectively borrowing money from the bank and agreeing to pay it back at the end of the month. If you don't, you'll get charged interest on the original amount.
That's why credit cards are best avoided while you're studying – if you don't have an income, you'll really struggle to repay the debts. This means the interest will build up quickly, leaving you owing serious cash.
Don't let the affordable-sounding minimum repayments trick you! Even if you can meet these each month, they're designed to clear barely any of the debt, meaning the cost of borrowing rockets.
If you borrowed £3,000 aged 21, and only made the minimum credit card repayments, you'd be 50 before it cleared.
Let that sink in for a while...