Depends on what stack you want to develop in. For an MVP you could try:

Ruby 1.9.2, Rails 3.1, HAML, SASS, jQuery, MySQL 5.5

It might not be the stack you end up with, but you'll learn enough building that to get started.

Start here with the free online book, it's as good of a place as any: http://ruby.railstutorial.org/