Some employers do not provide references as part of their own internal policies. Instead, the employer may only confirm employment including dates, salary and job title.
In this case, if you need a verbal reference or a letter, you should still ask every one of your supervisors to write you a letter even if they have a policy not to give one. Most often, despite a policy, some supervisors or managers will help you by writing a short letter.
When you give the name of a reference to be contacted, be sure to ask them not only for permission to give their name but also, ask them what they would say. Confirm they will give you a positive reference.
Although it may come as a surprise, in some cases when you conduct a reference, with permission, the reference is somehow extremely poor. Why would the candidate knowingly provide a reference that has only negative things to say?
If you are newer to the workforce, you could ask your teachers and professors to be a reference, or anyone who supervised you as a volunteer. Character references are not often requested but if they are all you have, then make sure to have them available.
To put your BEST foot forward, it is encouraged to call your reference to let them know to expect a call from a specific organization and for what role. Your call may remind them of you and your strengths!