Primary sources are first-hand accounts by participants of a particular event or materials produced at the same historical time period.
If you were examining racism in the 1911 edition of the Encyclopaedia Britannica, the article in the encyclopedia on the "Negro" would be a primary source. However, an article in the American Historical Review analyzing racism in the Britannica would be a secondary source. (Richard Marius, A Short Guide to Writing About History, pp. 14-15.)
Some examples of primary sources include:
Usually, library catalog records have at least one subject heading describing the general topic of the book, video, or other material. Subject headings can be subdivided to indicate further topical breakdown, geographical location, time period, or the form of the composition. Some of the form subdivisions that indicate the items is a primary source include:
Sources: collections of contemporary writings
Description and Travel: Travellers' accounts
Art, Literature
Be sure to evaluate the sites you find, particularly who created the site in order to determine biases and what information might be included/excluded.
Some libraries catalog their digitized archival collections in Williams WorldCat.
Note: some items will not be freely available or may just be collection finding aids.