What do you want to know? What has been assigned? If you need an overview of the subject, a general dictionary or encyclopedia will help. Check the print or ebook collection and look for specific people, places, events, and dates that can later be used in keyword searches of the subject:
Britannica Online (Note: for your reference only. Britannica cannot be cited as a scholarly source.)
Need a more detailed overview? Choose a subject specific encyclopedia or dictionary, Oxford Companion to Classical History in the library or online:
Early or medieval church history: NewAdvent
Philosophy: Plato, the Stanford University encyclopedia of philosophy
Music: Naxos Music Library
Ancient civilizations: Ancient History Encyclopedia
What do you want to know about the topic? It may be general at this point, but you can narrow, broaden, and refine it as you do your research!
Professors require that college level research projects are supported by scholarly sources. How do you know a source is scholarly? Ask yourself the following questions:
You will be utilizing other people's ideas and conclusions in your research and ethically and legally they need to get credit. Any information that is generally well known or references to well-known documents, such as The United States Constitution, does not need to be cited, but information that you glean from others must be paraphrased or placed within a quote, then cited. Lifting a paragraph out of WIkipedia or any source is unethical, illegal, and will always bring down a professor's wrath.
Check the course syllabus for your professor's preferred citation style. Citation assistance in available in the library and online at Online Writing Lab (OWL). Legal citations needed? Check out Georgetown Law's Legal Citations.