An annotated bibliography is quite similar to bibliographies/works cited you may have written in the past. The primary difference is that for an annotated bibliography, you are telling your reader a bit more about each source and your usage of it.
An annotated bibliography often DESCRIBES (includes 1-2 sentences about the main idea of the source), EVALUATES (discusses the strengths and weaknesses of the research and arguments), and CONNECTS (explains how you plan to use this source in your work- both content-wise (I plan to use this in my historical background, I plan to use the statistical data) and in approach (This aligns with the arguments in X source, this provides a well thought our counter-narrative that I will argue against).
Depending on your assignment, you might focus on one or two of these annotation-parts.
Taft College Annotation Information with Example