You may use the National Student Loan Data System (NSLDS) to review all of the federal student loans you have received. Your loan servicer is a company that manages the repayment services associated with federal student loans. They will assist you with selecting a repayment plan, loan consolidation, and any other requests associated with your federal student loans.
The contact information for each of your loans can be found by logging into NSLDS and clicking the link for the loan. It is important to contact your loan servicer if you are having difficulty making payments. For more information about loan servicers, you may visit StudentAid.ed.gov: Loan Servicers.