Mac OS X only starts –
Before installing RVM you need a compiler in order to install any Ruby version, for this, first check this post:
– Mac OS X only ends
After getting that done, you can go ahead and run these lines within the Terminal:
curl -L get.rvm.io | bash -s stable
And then this, to load RVM:
source ~/.rvm/scripts/rvm
If you want/need a more explained or other installation options, check https://rvm.io/rvm/install/