OK, let's say you wanted to find information about "indigo" people, that is people who supposedly possess certain psychic powers. (This was a question just now at the reference desk!) Where do you look?
The catalog for books - there weren't any books with the word "indigo" in the title that were about psychic phenomena (they were all about the plant, textiles...) However, there were books about pyschic phenomena, esp and so forth. Maybe those will help, for background at least.
Articles - Lexis for newspaper articles, Academic Search for articles. This was not so great at first, just using "indigo" for a search word - lots of hits on the plant etc. However, a quick google search found several sites about the "indigo child," that is children with these powers. Now that we had the phrase we could go back to Lexis and others and search for "indigo child," and get better results.
And it's that easy ;-)