An annotated bibliography is a list of sources on a particular topic.
Each source appears as a properly formatted bibliography-style citation, followed by an annotation.
An annotation combines summary + analysis of the source, so that the reader has a clear idea of what the source covers, its strengths, weaknesses, and why/for what purposes the source should be consulted.
When writing your annotation, think about the role the source serves in your research project overall. Does it provide background information? Evidence? An argument? A rebuttal to an argument? A theoretical lens or framework? You may refer to the ways in which your source will serve a purpose for your research.