Typically, a borrower will have Direct Federal Subsidized loans first, then Unsubsidized loans per year. If these don’t total enough to cover the cost of their education, then the borrower can move into Parent PLUS loans, which are loans that are taken out in the name of the borrower's legal guardians. The borrower can also move into private loans either with their current loan servicer or with another alternative loan servicer (typically, this is Sallie Mae).
You can find a listing of potential loan types and what they mean here on studentaid.gov.