This short video from the Lincoln Memorial University Library explains the what, why, and how of an annotated bibliography.

According to the Excelsior Online Writing Lab:

A bibliography is an alphabetized list of sources showing the author, date, and publication information for each source.

An annotation is like a note; it's a brief paragraph that explains what the writer learned from the source.

Annotated bibliographies combine bibliographies and brief notes about the sources.

More: https://owl.excelsior.edu/research/annotated-bibliographies/