Encyclopedias, dictionaries, and other resources to help you discover basic information—names, dates, definitions, summaries, etc. These are good places to start when narrowing or choosing your topic, and when beginning research on an unfamiliar subject.
Oxford Bibliographies Online give an overview of a topic, then an annotated bibliography of works on that topic. A great guide to use when starting your research or doing topic exploration. The music collection includes entries on composers, genres, and forms.