An annotated bibliography is a list of citations that includes a paragraph length annotation. This type of bibliography can help researchers determine the value of the source and how that source could potentially contribute to his or her own research. There are two main categories of an annotated bibliography: descriptive and analytical. They could also be called informative and critical.
It helps you learn about your topic. If you are to write an annotated bibliography, you will have to read your sources carefully, and be critical of them. It also helps you learn where your research fits in the larger scholarship of your topic.
It helps others learn about your topic. If you are writing a critical annotated bibliography, your insights will help others understand the topic and what resources could be useful to them.