A commercial bank is where most everyone does their local banking. This is in contrast to an investment bank. Commercial banks offer a range of financial products, including loans, mortgages, checking, savings, CDs, retirement products, credit cards, and more. These banks make their money from lending.
When you open a deposit account such as a saving, checking, or CD, you are basically lending the bank money. As a lender, you expect to be paid interest, which the bank does. Although it is a very small amount. The bank uses your funds as loans to its customers. Because the bank lends at a higher rate than the interest it pays on deposit products, it is able to generate a profit.