Citation tracking is tracing who has cited a particular paper. As a literature search strategy, it can be useful for identifying important papers, discovering who else is doing research on a topic of interest, and finding more recent research on a topic.
Citation tracking is also critical to impact factor, a measure of an article's, or entire journal's, influence on a field of research. The more citations a paper or journal has, the higher the impact factor.
Google Scholar is the best free resource for citation tracking. Under each citation in your search results, look for a "Cited by" link and click it to get citations of that article.
Google Scholar finds citations that are visible on the Web. As more and more databases make citation information publicly accessible, Scholar becomes more useful for citation tracking--but be aware that it won't find everything, and it will find a lot of articles that the library can't access. Use the Library Links option in your Scholar settings to link Scholar to PLU's collection (campus computers are already configured to do this).