FromWikipedia
Ruby on Rails, often shortened to Rails or RoR, is an open source web application framework for the Ruby programming language. It is intended to be used with an Agile development methodology that is used by web developers for rapid development.
To run Ruby on rails you first need to install Ruby, and RubyGems. By default, Rails includes the sqlite3 gem and is automatically configured to use it. Look for documentation if you want to use an other database.
You may want to have a look at this good tutorial
Please install what you need to run Ruby on Rails on your machine before the workshop, and fill this wiki section to let us know about the issues you might have found while installing.
I've found issues following the official tutorial, so i'd suggest the apt-get way :
sudo apt-get install ruby rubygems rails