Often it is helpful to look at examples of annotated bibliographies. For sample annotations and more instructions on writing annotated bibliographies, see:
Your professor may ask you to write an annotated bibliography rather than a paper. An annotated bibliography is a list of sources on a certain topic with a brief description of each source.
Each entry in an annotated bibliography should include all the information normally included in a list of works cited. Use the appropriate bibliographic format for citations (such as MLA, APA, Chicago, etc.) as specified by your instructor.
The bibliographic information is followed by an annotation. This annotation can be a few sentences or a lengthy paragraph that describes and evaluates the content of the source. If you have questions about how detailed or evaluative the annotations should be, ask your instructor.
Here's an example of an entry from an annotated bibliography. The citation of the book is in MLA style:
Bertot, Lillian D. The Literary Imagination of the Mariel Generation. Endowment for Cuban American Studies of the Cuban American National
This book-length work examines the Mariel generation of writers. Bertot argues that these writers most often comment on present-day Cuba, but their social criticism also attacks other times in Cuban history and other aspects of Cuban society. Bertot states that in the works of the Mariel generation of writers, Cuban society is in chaos and in trouble of falling apart because it is no longer in transition toward building socialism, but has failed. She notes that Reinaldo Arenas is the most prolific writer of this group, but other writers of importance are Roberto Valero, Carlos Victoria, Miguel Correa, Reinaldo García Ramos, and Juan Abreu. Bertot argues that these writers are different from the previous exile writers because they came from socialist Cuba. Bertot notes that after arriving in the United States, they characterized themselves as a literary group, creating a literary magazine, Mariel, a Magazine of Literature and Art. She states that the theme of freedom frequently appears in the Mariel generation Cuban-American writing, and that can be freedom of thought or creation and spiritual and sexual freedom. Another theme she notes is the struggle for survival, especially of the individual. Bertot’s book is essential to understanding the whole of Cuban-American literature by describing the works and themes of this group of Cuban-American writers.
(Example from: Cuban-American Fiction in English: An Annotated Bibliography of Primary and Secondary Sources by M. Delores Carlito. Lanham: Scarecrow, 2005.)