In each case, select "in subject" in the third dropdown under the white search box
If you have trouble, ask for the book Music Subject Headings, which is behind the circulation desk in the Music Library. It contains the correct subject phrases to enter for particular musical topics.
Search for journal articles on topics related to music - from traditional music to popular music to classical music. (EBSCO)
To get an overview of a classical music topic, try Grove Music Online. It gives background information and bibliographies.
Composer Resource Manuals take a detailed look at scholarship on individual composers. They include annotated bibliographies.