As the name suggests, an annotated bibliography is a bibliography, but one that includes a brief summary and assessment of each resource. In assessing resources, you want to comment not only on their quality, but also on how they fit into your own argument.
For more information on constructing annotated bibliographies, see these two excellent guides:
Many annotated bibliographies also require writing an abstract:
When getting started, I will sometimes Google my topic to help me find more vocabulary and ideas. Once you're ready to find scholarly literature, you'll want to use a library catalog, journal database, or Google Scholar to help you find appropriate sources, but a general Google search can be helpful in the brainstorming phase.