Remember that background information, such as biographies of authors, definitions of literary terms, historical background, etc., does not qualify as scholarly secondary source material in the field of literary criticism. They may, however, give you a better understanding of the context in which the author was writing.
Key definitions for writing in the field of English/Literature:
Primary source/material - In literature this refers to the novel, short story, play/drama, poem, or other literary piece(s) being studied. These should always be cited in the bibliography, but do not count as "secondary sources."
Secondary source/material - As described above, this primarily refers to literary criticism in the field of literature. Most English professors will be looking for literary criticism in the required sources section.
Literary criticism - This is not, as the name implies, merely individuals criticizing works of literature. Rather, literary criticism is articles, books, and book chapters in which scholars in the field argue their own analyses/theses about a primary source or sources.
The Oxford Dictionary of Literary Terms by 
The Routledge Dictionary of Literary Terms by Many of our best sources of background information on literature are available in full text online.
