You must be joking… seriously I hope your joking. That would be like taking a million steps backward.
I'm not familiar with spree but based on the what I do know about rails you will need to know some ruby. That is if you need to change the HTML.
Honestly, you are not going to get very far without learning some things about the command line installing ruby and rails.That is if you would like to set-up a local testing environment. Have you looked at the spree docs?
If those docs don't make any sense to you than you first need to step back and set-up ruby than rails on your machine w/ the proper gems. That in itself can be quit a task depending on the machine you are running.
I don't think this is really the job for a web designer not to mention a beginner. To even get started with rails you are probably going to need to dive into some amount of programming and command line fun.