I need help installing things to my RoR application

I'm trying to follow the lessons of the Ruby on Rails program but making some changes to make something I want to make for myself and I keep finding that my application falls apart any time I try to install anything I am not writing. So I can't install devise(I don't even get close to the same messages that are in the videos) and I can't install any other program like one I was looking at called forum monster. I can get them in the gem file and bundle it but when I go to run installs it just talks about missing the ORM. I know in programming you work to figure things out for yourself but I just feel like I'm too new at this to figure it out alone so any hints or advice? I run on a macbook pro if that makes any difference at all.

ETA: This is what my console is telling me when I try to run rails generate devise:install

/usr/local/rvm/gems/ruby-1.9.3-p392/gems/devise-2.2.4/lib/devise/rails/routes.rb:448:in `raise_no_devise_method_error!': Install does not respond to 'devise' method. This usually means you haven't loaded your ORM file or it's being loaded too late. To fix it, be sure to require 'devise/orm/YOUR_ORM' inside 'config/initializers/devise.rb' or before your application definition in 'config/application.rb' (RuntimeError)