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.
PC2001-3761 French language
PQ1-3999 French literature
PQ1-771 History and criticism
PQ845 Juvenile literature
PQ1300-1595 Old French literature
PQ1600-2726 Modern literature
PQ3800-3999 Provincial, local, colonial, etc.
For more in-depth information, see Library of Congress Classification Outline: Class P