Can anyone offer any useful distinctions between just plain Ruby and Ruby on Rails? I am trying to figure out whihc of these I should learn.
Ruby on Rails is a web framework that has been written in the Ruby programming language. If you don't take the time to learn the Ruby syntax, you will struggle with Rails. Not saying you must become an expert in all things Ruby, but you should at a minimum get comfortable with the basic object classes (arrays, strings, hashes, etc) and their corresponding methods. If you are just getting started, I would urge you to check out Chris Pine's site - http://pine.fm/LearnToProgram/ which covers the basics of the Ruby programming language, then you can start reading through the Rails Guides http://guides.rubyonrails.org/getting_started.html to learn more about the framework.
Ruby is a Language
Ruby on Rails is a Framework that utilizes Ruby
It is a akin to PHP (Language) and CodeIgniter (Framework)