In Feedback studio click anywhere on the paper to leave a comment.

Quickmarks are preset collections of feedback, for things like composition.

You can create your own sets of quickmarks.

Comments are freetext feedback that can be linked to highlighted text, click on the colour top right to change the highlight.
Drag the speech bubble to the side to keep the paper readable.

You can convert comments into quickmarks.

Inline text comments are direct text annotations on the paper, like writing comments between lines on a physical paper.