An annotated bibliography can help you learn more about your research topic and help you identify sources about that topic that are a good fit for your paper or project.
Annotated Bibliographies have two important pieces: the citation and the annotation. This is true in every citation style - MLA, APA or Chicago/Turabian.
The Purdue Online Writing Lab (OWL) describes the how to and why an annotated bibliography is useful and important in your research process.