Although geared to graduate students, the information on literature reviews is relevant to undergraduates as well.
Video produced by North Carolina State University. 
This video is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States license.
"Depending on the purpose of your bibliography, some annotations may summarize, some may assess or evaluate a source, and some may reflect on the source’s possible uses for the project at hand. Some annotations may address all three of these steps. Consider the purpose of your annotated bibliography and/or your instructor’s directions when deciding how much information to include in your annotations."
(from Purdue Owl website)
