To annotate is to make notes or commentary. In terms of class assignments, an annotation is typically a concise summary and/or evaluation of a source. The annotation can range anywhere from one to two paragraphs (or more) depending on the format specified by your instructor.
An annotation is typically a brief paragraph where you would . . .
Carefully read the assignment given by your instructor so that you know exactly what information they would like included in the annotation.
Check your understanding by answering these review questions. If you get one wrong, read back through the material and try again!