In Java/Tomcat I have a web.xml to define a "welcome-page" which usually points to some index.jsp. This means that if my root URL is http://www.mograbi.co.il/guy_mograbi it will show the page http://www.mograbi.co.il/guy_mograbi/index.jsp .
In Rails it works like this :
- Under your application root folder you will find the folder "public". In which you will see an "index.html" file - that default to "Rails Welcome" that looks like the IFrame I show below
- In folder "config" you will see the file "routes.rb" that is very important - I will dedicate a whole entry only on this file. You can define the welcome page like as such :
map.root :controller => "categories"
(for example). Read more about it here