You may start out with a "line of credit" agreement with a bank that allows you to create relatively small loans by the bank to yourself at a specified interest rate and under other specific terms. Of course you must repay these loans, with interest, and that's how the bank makes its money.
If you fail to repay the bank, the bank may close your account and demand that you immediately repay all the money you owe it. A "closed line of credit" is a pretty sad thing.