To have the option to sell phone cases you just need to add prices to them the same way as you do the prints.
The cases are on http://pixels.com and premium sites only
Pixels.com is going to become the parent website that sits above all the other websites. As we introduce new products (e.g. iPhone cases, calendars, puzzles, etc.), each new product will appear on Pixels.com. The "fine art" domains will continue to only sell products that fall under the "fine art" heading (e.g. canvas prints, framed prints, etc.)
Just log in using your normal details
On the top right menu, when logged in, there is a drop down with everything you need for the site
BEHIND THE SCENES is for all the tools you need to set the site up and PROFILE is where your site is. I know it helped me when I first joined to just play in there a while before doing anything else.
At this time you are searching for DOMAINS where you can learn more about the sites