Also look at the footnotes and bibliographies of helpful secondary sources; they may reference primary material that you can locate and use.
From the American Library Association's Reference and User Services Association, this guide is designed to help students find, evaluate, and use primary sources available through online archives and libraries.
Combine keywords relating to your topic with keywords indicating a primary source. For example, search for "Civil War And personal narratives" or "Dust Bowl AND letters."
Think about the time period you’re researching and use appropriate keywords.
As you enter your keywords, consider whether primary sources are really going to give you the information you’re looking for.