A credit card lets you spend the bank's money and pay it back later. Used well, it's convenient and can build a good credit history. The trap is the interest: if you pay only the "minimum due," the rest carries over and is charged interest that is often 30–40% per year — one of the most expensive debts most people ever take. The golden rule: pay the full statement balance every month, not the minimum. Do that and you pay zero interest and get the benefits. A card is a tool — powerful if you control it, dangerous if it controls you. Never treat your credit limit as extra income.