It's actually very simple. You list your clipart on the site through the easy to use Shop Dashboard. Buyers search for clipart by browsing the site using various methods - by category, by price and by shop. Once they find your clipart and decide to purchase, your shop account is credited with the sale.
That's it in a nutshell! Oh yeah, did we mention that as an Artits Shop, you get 85% of each sale?