setting up MarketPress eCommerce plugin for my MULTISITE

how do i set up my MARKETPRESS ECOMMERCE plugin like it says in the description to take a percentage of sales from my users?

i want to offer the Marketpress plugin to my users and have it like Eetsy and Ebay where i take a percentage...but im unsure of how to set this up...any advice? any links to documentation?

Thanks in advance!!