Reference materials are a great way to get a broad overview of background information on a topic. Start with reference works to help you choose or define a research topic. Reading some basic background information will lead you to new terminology and concepts which you can then use to search databases or the library catalog for more specific information on a narrower portion of the topic.
In addition to a print copy in the W.E.B. Du Bois Library, we have access to the Diagnostic and Statistical Manual of Mental Disorders, fifth edition (aka DSM-5) through the database Psychiatry Online.