A bibliography is a list of sources (books, journals, Web sites, periodicals, etc.) one has used for researching a topic. Bibliographies are sometimes called "References" or "Works Cited" depending on the style format you are using. A bibliography usually just includes the bibliographic information (i.e., the author, title, publisher, etc.).
An annotation is a summary and/or evaluation. Therefore, an annotated bibliography includes a summary and/or evaluation of each of the sources. Depending on your project or the assignment, your annotations may do one or more of the following.
From Purdue OWL (The Purdue OWL. Purdue U Writing Lab, 2016.)
Lamott, Anne. Bird by Bird: Some Instructions on Writing and Life. Anchor Books, 1995.
In the sample annotation above, the writer includes three paragraphs: a summary, an evaluation of the text, and a reflection on its applicability to his/her own research, respectively.
From Purdue OWL (The Purdue OWL. Purdue U Writing Lab, 2016.)