Primary sources are generally defined as first-hand accounts of events. A primary source is an original work, not derived from other sources. They may be first-person accounts, such as diaries, letters or interviews, or official government records or court records. Visual records, such as painting or photographs, as well as films, television programs and even advertisements are also primary sources.
Look for primary sources in ThomCat [or any library catalog] by using the following keywords in combination with other search terms relevant to your topic:
Example: Zapatistas AND sources