rails

I do gem install rails -v 3.0.5 I get :succesfully installed rails-3.0.5 installing ri doc installing RDoc doc I do $ rails -v I get : $ rails commande introuvable I am : /usr/local/bin/erb-ruby-1.9.2-p180@rails3.0.5 I am stopped. I dont continue. Why. What i do. Please help me Thankyou