A bibliography is a list of sources (books, journals, Web sites, periodicals, etc.) one has used for researching a topic. An annotation is a summary and/or evaluation. Therefore, an annotated bibliography includes a summary and/or evaluation of each of the sources.
Your annotations may do one or more of the following.
The bibliographic information: The bibliographic information of the source (the title, author, publisher, date, etc.) will be written in APA format.
The annotations: The annotations for each source are written in paragraph form. The lengths of the annotations can vary significantly from a couple of sentences to a couple of pages. The length will depend on the purpose. If you're just writing summaries of your sources, the annotations may not be very long (2-3 sentences).