A loan agreement arranges all the legal aspects of a business loan. It covers among other things the amount to be borrowed, how much interest the debtor has to pay and how and when to repay the loan.
In the loan agreement you will agree on the amount to be borrowed. But you also make agreements about when and how the loan will be paid out.
Almost always there will be interest on a loan. In many cases, this is even a tax obligation. In the loan agreement you make agreements about the amount of the interest. Over time, a loan will have to be repaid. We call that repayment. This can happen all at once, but you can also agree to repay an amount periodically.