Simple:
* The professor provided a helpful reference for my research paper.
* Please include a reference list at the end of your essay.
More Complex:
* The author's use of literary references added depth and complexity to the story.
* He received a glowing reference from his previous employer.
* The witness's testimony was contradicted by a reference in the police report.
Figurative:
* The movie was a blatant reference to classic films from the 1950s.
The best sentence for you will depend on the context of your writing.