All professors have different expectations about the length and contents of annotations. Be sure to check the assignment sheet or ask your professor what they require for your annotated bibliography.
Descriptive annotations focus on describing the cited items and may include information such as:
A reference list is a list of citations to books, articles, and other sources used while researching a topic. Reference lists may also be called "Bibliographies" or "Works Cited," depending on the style manual used.
An annotation is a summary or evaluation.
An annotated bibliography is a reference list/bibliography with annotations for the items cited.