Primary sources are contemporary accounts of an event, written by someone who experienced or witnessed the event in question. These original documents (i.e., they are not about another document or account) are often diaries, letters, memoirs, journals, speeches, manuscripts, interviews and other such unpublished works. They may also include published pieces such as newspaper or magazine articles (as long as they are written soon after the fact and not as historical accounts), photographs, audio or video recordings, research reports in the natural or social sciences, or original literary or theatrical works.
Primary: First-hand account of an event, an original work
Secondary: A summary, interpretation, or analysis of something else
Tertiary: Usually a combination or collection of primary and secondary sources
Often in English Literature studies your primary source will be the text (novel, play, poem) you are analyzing.