Learn all you can about your topic first. Check your text book, in-class materials, Wikipedia.org or the library database Credo Reference.
Gain a broad overview of your topic, learn the important names, facts, or keywords that define your topic.
You can look for books in the library catalog to find titles (or chapters within books) that deal with your topic.
Start linking keywords together in database searches. Look for general articles and move to scholarly peer-reviewed works.
Chase Footnotes, find more sources. Try a variety of databases. Track down clues wherever they lead (don't just settle for the first couple hits). And always know you can ask a librarian for help.
Searching the Web
Searching Google will yield tons of Web sites. To narrow the playing field try clicking on
"Advanced Search"
Here you can limit to
"Search within a site or domain"
e.g.: search for "Amy Tan" within ".edu" sites
What are they?
These are various databases that provide published sources.
Why use them?
Using a published source will likely produce credible information.
How do I know which one to use?
It all depends on the kind of information you seek.
Covers all subjects and many types of resources, with both scholarly and non-scholarly articles. A good place to start.
Provides information on social issues from diverging points of view.