You're probably familiar with cited reference. These are the articles, books, and other resources that the authors used when writing their piece. They are listed in the footnotes or at the end or an article or book. These cited references allow you to move backwards in the research process and see the work that influences and supported the original piece you found.
Citing references allow you to move forward in the research process. These are resources that are published after the original piece and cite it in their reference or work cited lists.
Citing references are a great way to find more current, related research on your topic. You'll want to be as up-to-date on your topic as possible, and citing references are going to be more recent than the original piece. Also, since the citing references used the original piece in their work, it's very likely that the topics are related. So if the original piece was useful to you, chances are good that the citing references will be as well.
Two databases specialize in tracking citing references. One is Web of Science. Despite it's name, Web of Science includes millions of scholarly articles in the sciences, social sciences, and arts and humanities. Google Scholar also includes citing references in its database of articles and books.
More and more library databases are also starting to track citing references. While these are more limited than Web of Science or Google Scholar, they can still be useful. Look for "Times Cited" or "Cited By" links in the records of useful articles in your favorite subject database.
If you've already found a great article and want to know if it has been cited by other, more recent schoarlyl articles, try searching in Web of Science.
To find other citing references beyond Web of Science, including books, try Google Scholar