It is a good idea to see if relevant chapters of your textbook, or articles in reference books that you find, have a bibliography/works cited/references list. If they do, go ahead and mine them for articles, books and other kinds of information sources to use in your research.
Citation chaining (sometimes called Reference Mining), like descriptor chaining, is another way to expand your search. It involves reviewing the bibliographies/works cited/references list of particularly relevant articles from your search results list in order to identify additional relevant articles.
If you have a good article, review the citations or references for other potential sources. Remember these citations were used to write the article, so if the article is relevant to your topic, the citations will likely be too.
This video by McMaster Libraries provides an overview of the research tool citation chaining, including its benefits and limitations.