Help Marketpress- Already registered Domain & Hosting (Not with you, do I have to go through you

Help: I already have domain, theme & hosting all set up. (Not through you) I have premium package.

I want to add marketpress and a few other plugins to my site. I uploaded the marketpress to my site and it says error.

Please help, I am not technical. I need easy steps.

This is what I want- please tell me the steps I need to get to this point:

People to sign-up on my site to sell their stuff
Them to be allowed to list as many items as they want
It will allow for them to add descriptions along with pictures
It would allow them to set their own price
Then paypal would work the splitting of the funds
Is there a way to charge a yearly fee to allow store owners to list their products

Believe me, I have read and searched. I am still not getting a totally understanding. I want it to work like ETSY. Where Etsy makes a profit off of each sale. ALL customers set up their own store WITHIN my site.