Sometimes wandering the shelves is useful. If you can find one book on a topic, others like it will be sitting on the same shelf. Be sure to look in both the Reference collection on the first floor for general helps like encyclopedias, and in the circulating collection on the second floor for books you can take with you. These numbers work for most other academic libraries as well.
Class PC5001-5498 Portuguese language
Class PQ9001-9999 Portuguese literature
subclass PQ9000-9129 History and criticism
subclass PQ9131-9188 Collections
subclass PQ9189-9326 Individual authors and works
subclass PQ9400-9999 Provincial, local, colonial, etc.
For more in-depth information, see Library of Congress Classification Outline: Class P