Annotated bibliographies are written to demonstrate an understanding of specific literature sources available on a topic. They are presented in a general format of a bibliographic citation, followed by a brief paragraph that may be a description and/or evaluation of the work. Check with your professor for specific requirements regarding:
Here are a couple links to very useful guides that assist with understanding how to write an Annotated Bibliography:
Purdue OWL - Annotated Bibliographies
http://owl.english.purdue.edu/owl/owlprint/614/
Annotated Bibliographies (from The Writing Center, University of North Carolina at Chapel Hill)
http://writingcenter.unc.edu/handouts/annotated-bibliographies/