"Pearl Growing" is the concept of using one really great resource as a starting point to find similar resources. For example, if you find one article that is on your topic, you can then click into the record. What subject headings are used? Are there keywords in the abstract that could be useful to your search? What about the author -- have they written other articles on the topic?
When you find a great article, another method for finding similar articles is to scour the bibliography for related references. This will lead you to other resources, which in turn may lead you to even more references. This is a great way to find citations that might not be indexed in large databases or grey literature (see the next section for more information on grey literature). Sometimes all it takes is one really good journal article to get you snowballing. You might hear other terms for this as well, such as "hand searching," but snowballing is my favorite because it is such a great metaphor for this activity.
When you find references in a bibliography, you are looking at older research -- stuff that was written that influenced the newer article or book. But some databases, such as PubMed and Google Scholar, allow you to flip this and search for newer research. If you've found a good article, you can try searching for it in Google Scholar. When you find the article, there will be a link that says, "Cited by ___," with the number of found citations. If you click on the link, you will see all the newer citations that have referenced this article.