@ variables in Ruby on Rails
title is a local variable. They only exists within its scope (current block)
@title is an instance variable - and is available to all methods within the class.
You can read more here:http://strugglingwithruby.blogspot.dk/2010/03/variables.html
In Ruby on Rails - declaring your variables in your controller as instance variables (@title) makes them available to your view.
Use @title in your controllers when you want your variable to be available in your views.
The explanation is that @title is an instance variable while title is a local variable. Rails makes instance variables from controllers available to views because the template code (erb, haml, etc) is executed within the scope of the current controller instance.
The difference is in the scope of the variable. The @version is available to all methods of the class instance.
The short answer, if you're in the controller and you need to make the variable available to the view then use @variable.
For a much longer answer try this: http://www.ruby-doc.org/docs/ProgrammingRuby/html/tut_classes.html