As you can see in the above image Users are selected in the Commission Based.
After selecting the Users based commission set the commission on Level Tab:-
Add a new level by pressing Add new Level button.
You will find the below screen.
you can make how many levels you want.
Note:- The First level should always Become an affiliate if you are making a level using this Become affiliate criteria
because when the user registers that level which has become affiliate criteria assigned to the affiliate.
As you can see in the above image 2 levels declared are explained in the above steps.
If the user has a total sale of 800$ and 20 successful referral so now the affiliate acquires 2nd level and start receiving a 20% commission on the product price.