An annotated bibliography is more than just a brief description of your resource. While it is tempting to use the article abstract in your annotated bibliography, it will not provide you with all the aspects of a well done annotated bibliography entry.
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:
Your annotated bibliography may include some of these, all of these, or even others. If you're doing this for a class, you should get specific guidelines from your instructor.
This information and more can be found through the Purdue Online Writing Lab (OWL).