What is required?
How many sources will you need? Look for more than the number your assignment indicates in case you can't locate all the items or some turn out not to be useful.
When choosing a topic for your research, take care to select one that is manageable.
Too much information can be just as problematic as too little.
To avoid an unmanageable topic, spend some time "reading around your topic" with some of the sources on the Background Reading tab, such as subject and general encyclopedias.