Multisite/ using numerous themes

http://www.staceyemiliou.com

Basically i want under ‘art’ and ‘shop’ to have the URL as my other domain which i have set up on the host godaddy and linked it to my prime domain (www.behindmyeyeball.com) – i don’t want to link to the domain as it has no hosting/nothing on it just the URL.

I also ideally would like another theme installed as well as the other one- i use elegant themes so i can use my behind my eyeball logo and set it up with a shop theme.

Which is the best and easiest way to go about this- i have NO experience and no idea where to start or how to even start using my plug ins.!

Thanks