Annotation is adding notes to a text as you read - not just highlighting! You are actively reading & interacting with the ideas in the text. Think of it as "showing your work" just as you would for a math problem or as having a conversation with the book!
When you arrive on campus in the fall, teachers will be engaging the required books in a substantive way in the classroom, so you should bring your annotated copies with you. You can find resources here to help you with annotations.
Don't forget - annotate only your own copy of the book!