Ruby on Rails (hereinafter just rails) is a web framework written in the Ruby language.
There are several articles about the language on Habré, I think it will be useful to read them if you have any difficulties - read Wikipedia, the best book about the language is Programming Ruby, the best book about rails is Agile Development with Rails, and ask questions.
Let's start with installing Ruby and Rails.
Windows users need to download and install the One-click Ruby installer.
For Linux (Ubuntu) users, installing Ruby is even easier:
<code class='sh' lang='sh'>$>sudo apt-get install ruby rubygems rake</code>
Making Sure Ruby Works
<code class='sh' lang='sh'>$>ruby -v
ruby 1.8.5 (2006-08-25) [i486-linux]</code>
and put the rails:
<code class='sh' lang='sh'>$>gem install rails --include-dependencies
All you need to get started is a text editor with Ruby syntax highlighting and the ability to execute commands from the console.
For IDE lovers, I can advise Aptana, I write code in it (I just like Eclipse :).
I will give all examples for the console, what to do in Aptana should be clear, I can write about it separately.