Honestly. Thought it was going to be easy. Using railsinstaller or the instructions found in a variety of places. None of which seemed to work. And all of which involved installing RVM as part of their broken processes. So the simple way? Just use RVM and have it do the whole thing.
Go here: https://rvm.io/rvm/install
for instructions. But really just type this into a terminal window:
\curl -L https://get.rvm.io | bash -s stable --rails Enjoy a cup of coffee. Then you should be done.