Some of the course assignments are peer reviewed which means you'll get feedback from other people taking the course. You'll also need to review other people's assignments and give them feedback.

Your grade for a peer reviewed assignment is based on the grades your peer reviewers gave your assignment.

You'll be asked to start giving peer reviews as soon as you submit your own assignment. You'll need to do the required number of peer reviews for other people's assignments before your assignment will be complete.

For more information on peer reviewed assignments, see Coursera's Help Center

See also, How do I get my assignment reviewed on Coursera?