@Tenzimom, Every month you’re charged interest on the principal balance of your loan. If you pay more than the minimum payment the principal is reduced more than if you pay the minimum. A lowered balance means less interest.
A real life example: when my eldest was a sophomore my spouse was injured and lost 6 months of work. We took the $6500 student loan to not tie up our cash. The loan payments don’t start until next Dec, but I started paying it right away. I noticed that if I paid $100/month $92 was applied to the principal and $7 to interest. If I pay $130 or more it’s all applied to the principal.
If you have more than one federal student loan you can request that anything you pay over the minimum be applied to the loan with the highest interest rate. The subsidized and unsubsidized rates can be different, and they may change from one year to the next. The interest rate for the unsubsidized was 4.29% fixed. The subsidized part is 3.76% fixed. So pay attention to the interest rates too.