Affiliates comission

Hi there WPMU team,

Pardon I just would like to know how can I set up comission percentage with affiliates plugin?
I have 3 membership subscriptions or let say 3 products the affiliates advertising with
2, 5, and 10 dollar prices and wanna set average of 20% comission after the sells. I went through the plugin but I couldn't find the way how to set it. Could you be kind and help me regarding this problem?
Thanks and good day!
Sandor Sz.