Sometimes you may be interested in a topic, but don't know much about it. If that's the case, then some background reading, either in books or encyclopedias, can be very helpful.
Reading an article in an encyclopedia or a chapter in a book can tell you what's important to researchers on your topic, and can help you narrow your topic, which will be helpful when you start searching for sources.
That's why people like Wikipedia so much--it helps them learn more about things they're interested in.
Use the ebooks and encyclopedias on this page much like you would encyclopedia--to get an overview of what you're interested in.
Take a Look at the Other Parts of the Psycinfo Tutorial: