Biographies of individual composers are shelved at ML 410, alphabetical by composer. Collective biographies, which include multiple composers, are at ML 390.
Most biographies emphasize the composer's life, but many include information about and even some analysis of the music.
Books specifically on appreciation and analysis of composers' works are at:
See also the Biographical Information page of this guide.
Guides to analyses:
Music Analyses by 
Analyses of Nineteenth- And Twentieth-Century Music, 1940-2000 by Research guides (also called bio-bibliographies) contain biographical information and list books, articles, and other sources about composers and their works.
Shelved in Reference at ML 134, alphabetical by composer.
These books list a composer's works, usually with the opening phrase of music (incipit), information on manuscripts, published editions, and sometimes bibliography. Useful for identifying a piece or verifying information about it.
Shelved in reference at ML 134, alphabetical by composer.
These are generally the most authoritative editions of a composer's works. They are shelved at M 3.
To find a work in the editions: find the composer's biography in Grove Music Online (in Oxford Music Online) and go to the list of works. It usually indicates in which volume of the edition(s) a work appears.
Access to Oxford Music Online is under the Dictionaries & Encyclopedias tab above.
Composers' thematic catalogs (Ref ML134) may also have this information.