Most employers will ask you to give them three or four people as references and specify the relationship you had with those people. Some employers are going to ask you for specific people, like previous supervisors, customers, or maybe peers… be sure you’re prepared to provide these different kinds of references when asked.
As you begin your job search, it is a good idea to think about who you might give as a reference in just about any interviewing process… I would recommend calling those people to let them know you’re actively looking for a position, and ask their permission to use them as a reference… it is very rare, but I’ve seen situations where the people who candidates thought would be a reference for them refused to do it… after they give you permission, inform them you will let them know who might be checking your reference, what kind of position it is, and exactly what in your background he should emphasize when the reference is checked…