Multisite Marketpress

Hi all, I am new (total wp noob) and working on my etsy clone site. I finally had some breakthroughs in my understanding of all of the themes and plugins and i am no longer totally overwhelmed. Thank you so much for all your prior posts and recommended readings.

Please take a look at my site so far. Of course still have tons to do.

handmadetampabay.com

I have some questions.
How do I get the buy and sell pages to function? I don't see what I have to do to make the shops and products show up. I suppose I need a few more test shops to test this out?

Also, I don't really understand the shortcodes that well.
For example, I made a page called Discover, the idea is that random shop's products will show up on the page. I made a shortcode [mp_list_products paginate="true" page="1" per_page="10" order_by="rand"
but it doesn't seem to work.

How do I get rid of the 'Leave a reply' box on each page?
How do I edit the left side Categories/popular products/meta tags widget?
Where do I make the sign in form?
Where do I make the register form?

I have marketpress, gridpress, membership premium, network wide menu, prosites and sitewide admin (header/footer) active

Plan on activating buddy press as well.

Thank you for any help you can provide.