How do you think banks make money, how does a bank make money to pay its employees and business operational?
Does the bank rely solely on interest on loans from banks?
Banks invests money you deposit to a business, loans, etc. in order for them to gain. Banks have protocols about how much they can invest. For instance, you deposited $100. The bank will hold (let us say) 10% of the deposited amount and store it in their vault. The remaining 90% goes to their projects, investments, or whatever is their way of earning. So basically, your money makes the bank and the project they are investing in alive.
The 10% stated above varies from different banks depending on their own protocol.