Find background information on your topic so that you'll begin to understand the who, what, when, where, why and also the vocabulary surrounding your topic. This will help you narrow your topic to something manageable and will give you a bit of context so that you can decide more easily where to search later. You can begin in Gale Virtual Reference Library, a collection of (mostly) encyclopedia articles, which are short overviews of a topic. Check out the other listed resources as well.
