Primary means written at or near the time of the historical event.
Secondary means written many years later, probably by a scholar researching the historical event.
You can find some primary sources in books. Below is a list of relevant subject headings. When searching for these in the catalog, try adding "sources", "documents", "correspondence" or "letters" to your search.
A repository for digital collections. Items in the public domain (works published before 1923) are freely accessible online.
A digital library of Internet sites and other cultural artifacts in digital form. Includes digitized books, periodicals, media, and more.