What are credit cards? - A small plastic card issued by a bank, business, etc., allowing the holder to purchase goods or services on credit.
Why do people use them - When used responsibly, a credit card can help you build a good credit history, allowing you to get loans at favorable interest rates, cheaper insurance and even a new cellular plan. Credit cards can also help you earn rewards on your everyday purchases and protect those purchases in case of theft or damage.
(Google)