Once a participant is done with the review, they can indicate that they have finished the review. This helps the moderator understand review progress. Note that the process for finishing a review is slightly different for moderators, approvers and reviewers.
As you go along, you can mark items you have reviewed with a green check mark to keep track of them. When a moderator closes a review or the review deadline is reached, you will see a window showing the number of comments you contributed, and how many items in the review you marked reviewed. You can add any final comments on the review here and Finish the review.
Note: A reviewer can reopen their review (Actions > Reopen review), if the moderator has not closed the review.