Annotated bibliographies are made up of two parts: citations (a bibliography or "works cited") and annotations of those citations.
A citation is a formal way of documenting a source. It's how you give credit for other peoples' ideas and give context to your own ideas. There are multiple ways to format these citations (known as "styles"); the style you use depends on your subject area and professor's expectations. For this assignment you will be using Geological Society of American Bulletin (GSA) style.
An annotation is a space for you to summarize and/or evaluate an article. Writing summaries is a great planning step in the research process and also allows a place for you to demonstrate your work. Annotations will also make your life easier when it comes time to collect your ideas to write!