Primary sources are anything created during the time period under consideration: published books; unpublished letters; photographs or drawings; music or song lyrics; clothing; objects of everyday life; etc.
Academic libraries and historical museums often try to digitize primary source collections held in their archives and special collections in order to make them available to the widest possible audience.
You can analyze and interpret the websites (or portions of websites) of organizations or advocacy groups as primary source materials.
Examples:
Books in Primo are assigned Library of Congress Subject Headings. In many ways, subject headings are a form of tagging, in that they represent the content of the material and provide ways for you to efficiently locate more materials that are conceptually related.
Library of Congress Subject Headings are also quite useful for discovering primary sources. The following subheadings usually are added to indicate that the material is a primary source: sources, personal narratives, correspondence, diaries, manuscripts, or notebooks. Topics that generate heated debate may be cataloged with the subheading: controversial literature. Once you've discovered the subject heading for secondary sources, try adding one of the primary source subheadings to see what you find.
If you have specific authors and/or titles, it's usually smarter to do an advanced search in Primo:
Dawkins, Richard, The God Delusion
Remember that groups can function as authors, too:
Historians use newspapers as primary sources. Depending on their research questions, they may analyze all parts of a newspaper: articles, editorials, reviews, analysis, and advertisements.