Use the Add Text tool or the Freehand Draw tool, on the toolbar when checking your students' submission to write feedback next to individual questions.

These two tools allow you to leave comments next to your students' work.  If your student left a lot of writing or text boxes on their paper, click on the box next to ‘Show student elements’ (PRO) and extra freehand writing, textboxes, and highlights will disappear. 

*Remember: You can also leave a comment that the student will see at the top of the assignment by clicking on the "Comment" on the left hand side of the submission.