Three types of comments exist: Reader, reviewer, and change comments.
You can add a comment by clicking on Add Comment, typing the comment's content in the field, and clicking on the validation icon.
It is also possible to add a comment by highlighting the text that you want to comment on and clicking on Add a comment. This will copy the text selected into the comment section.
Reader comments are visible to other readers as well as in the editor by clicking on Monitor --> Reader comments:
Note: If you cannot add a comment, it is because your admin deactivated comments for all or certain manuals.