Vendor

I installed Opencart and auction module. I dont have anything to sell but what im im going to do is to invite vendors to auction their product to our site. My problem is i dont know how to make them sell there. Someone that helped me before to install the auction module that we just have to change/config the user permission for able the vendor to sell but he is gone now. Is't true? How? I'm confused with the configuration because they might have access to other options that they dont have to. I dont have enough funds to buy another extension after i bought auction module. Can you recommend an extension that is free or the cheapest? Or please help me set up the permission. Thank you