Primary texts are usually works of fiction, poetry, or drama, sometimes historic essays, sermons, speeches, etc. A typical research paper analyzes one, two, or more primary texts. The danger of involving too many texts is that the analysis is spread thin.
Background sources refer to handbooks, encyclopedias, and companions to literature that provide basic generic, biographical, or historical information. In libraries general encyclopedias and dictionaries are located in the A shelves of UHCL's Neumann Library's Reference section. Specialized literary encyclopedias and handbooks are found on the Reference section's PR and PS shelves. On the Web, such sources would include Wikipedia and other more or less specialized literary websites providing common knowledge or basic information on varied topics.
Secondary sources refer to critical articles about particular authors or texts. (When you write an analytic / research paper, you are creating a secondary source.)
Secondary sources may take the form of articles or books.
Articles may be found in journals or bound collections of essays. Books of secondary research (histories and analyses of literature) are found on the regular PR and PS shelves of the library, or on the Web through JStor and other web-accessible journals or books.