To give back some and since I was bugging people to update this thread
As of Summer II 2024, this is how YP undergrad classes work:
There are reading assignments and videos. These must be clicked to proceed to the milestone. Note: The moment you click the link, it is marked as read, but you can spend as much time reading/viewing as you like, and you can go back later to read/view again during the session. After the session ends, you no longer have access to the course materials.
After the course materials, you usually reach a milestone assignment, or less commonly now, a quiz. The milestones can take the form of an essay (more common in my experience) or an Excel file or other MS Word documents. The quizzes allow a few tries (I think 3?). I only encountered quizzes in one or two of 14 classes.
When you have turned in all milestones for a class, you can view the requirements for the final, but you can't submit the final or draft until all milestones are graded with a grade of 3 out of 4 or higher. If a milestone is graded below 3, you must improve it and resubmit until you achieve a 3 or higher. You also must pass any quizzes with, I think, 80% or better.
Important, there are reportedly some classes where the final requirements you can see are more complete after the milestones are graded, so you should always check the final requirements after all milestones are graded before turning in your draft or final. I did not encounter this, but I always checked based on what other people experienced in some classes.
As the thread title says, you definitely should turn in a draft, because the grading and feedback you receive for it make it more likely that your actual final will get a good grade. The draft is optional but I wouldn't skip it unless I had some urgent reason to do so, like if I was trying to complete a class on the last day and couldn't wait to get draft feedback. It is very risky to skip the draft if you want good grades.
When you turn in either a draft or a final, you can then request another class. There is no limit I'm aware of for how many classes you can have open, except that only up to two at a time can be at a state prior to draft submission. Classes don't technically close until the end of the session, so I technically had 14 classes open late in the session.
By policy, the only grade that affects your class grade and ultimately your GPA is the final assessment grade. There have been some instances where instructors have not followed this policy, and factored milestone work into the course grade. That didn't happen in my case as far as I know, but you should be aware that it is possible.
I have read that graduate level classes differ in two structural ways. One is that you can have only one class open pre-final submission at a time. The other is that there are no drafts. However, this second point is rumored to be changing for Fall II. I have not done MAOL so I can't personally vouch for any of this paragraph.
Hope this helps!