The assignments are a chance for students to practice what you are teaching them in the video lectures, and they give the students and you feedback on their level of understanding. This aspect of the open online course is what sets it apart from other kinds of open courseware.
There are four ways the Coursera platform allows instructors to assign student work: in-video quizzes, stand alone quizzes/exams, programming assignments, and peer reviewed work. Each method asks students to demonstrate certain types of knowledge and it is worth considering what you want students to get out of your course before you decide which ones make most sense. Your standards for successful completion of the course will also be tightly linked with your goals and will inform how much emphasis you place on each of the assignments.
For more details on how to set up these different types of assessment, you can go to the Coursera supporting documents if you have administrative access. If you do not have administrative access but would like to, please contact CTL.