Annotated bibliographies are lists of sources, with a brief description of the source below each item. Basically, it is a references list with a descriptive paragraph below each citation
Citation: This should be the full APA citation for the resource. It should look identical to citations found in a references list at the end of a paper. Each citation should be alphabetical order.
Annotation: This is a short paragraph (or two), describing, analyzing, and critiquing each resource. The annotation goes directly below the citation. The annotation should be more in-depth than just a summary. There should be an analysis of the resource that goes along with the description. The annotations shouldn't just describe what the source is about, but also how it adds evidence to your specific research question. What is unique about the information presented in this source that will help build an argument? There should also be an evaluative description of the resource that discusses the appropriateness of the resource. It should answer questions like currency, author credibility, suitability of source type, types of evidence presented, and source objectivity.
(The above example came from Purdue's Online Writing Lab).
Feel free to download a copy of this example for future use. Please note that the superscripts are not meant to be in a real annotation. They are simply notes on how to best craft one - your bibliographies should not contain footnotes. The citation is in APA format, but it can be any style.