During a Session, you can assign ratings and comments to a Candidate. To access this, select the Participant List in the bottom-right corner of the session:
From here, click on the Display Reviews clipboard icon, next to the candidate that you would like to rate.
This will display the list of Rating Criteria (set up when creating the Project) as well as a Comment box. Simply click on the Rating Scales, and type in the Comment box to provide your review. When you have made any changes, you can click Update to save them.
Once you've updated your changes, you can click on the Clipboard icon for any other candidates to submit a review for them as well.