To give feedback to students as the teacher:
Go to the results tab within the assignment.
Find the student you would like to give feedback to in the student list on the left side of the screen.
Once you've clicked on the student you'd like to give feedback to, click Give Feedback on the right side (highlighted by the red arrow).
You'll be taken to the another split screen with the students submission on the left and the feedback rubric form on the right.
You will give feedback using the same rubric that students used.