The online version of Oxford Music Online contains the New Grove Dictionary of Music and Musicians, which is a great place to start your music research!

The same resource also includes the the Oxford Dictionary of Music, New Grove Opera, New Grove Jazz, and the Oxford Companion to Music.

Search for broad categories: composer name, genre, city, etc.

A good exercise to get to know your topic is to read articles on it from a few different types of encyclopedias.  You might start by searching for information in a specialized encyclopedia set. Also check out the Reference List or Works Cited in each article for more information on topic.