These literature databases include many different types of sources. In addition to journal articles that critically discuss specific works of literature ("literary criticism"), there are also overview essays from literary reference sets, biographical essays, book reviews, etc.
Your instructor may prefer that you select only those articles that are strictly considered to be literary criticism. If you have any doubts about what sources you should or should not use, it is best to check with your instructor.
The library has additional print sources that may contain critical articles about your chosen work or poet. However, keep in mind that critical articles on your particular work may be very limited or nonexistent. Ask a librarian for help if you are having trouble locating information about your poet or poem.