Assume some background knowledge on the part of the reader, such as an understanding of subject-specific terminology and concepts, an ability to interpret complex statistics, familiarity with prior research, etc.
Primary materials are different for every discipline.
Secondary Materials are books or periodical articles that synthesize and analyze an author's findings who has examined primary materials. If you consulted books of literary criticism on the poet's work and biographies of the poet's life, you would be using secondary sources.