If you've already installed devise into your app, and want to add "confirmable" later, instead of running:
rails generate devise:views
as mentioned by Piotr, run
rails generate devise:views confirmable
to produce only the views needed for "confirmable".  You'll see output like this:
rails generate devise:views confirmable
    invoke  Devise::Generators::SharedViewsGenerator
    create    app/views/confirmable/mailer
    create    app/views/confirmable/mailer/confirmation_instructions.html.erb
    create    app/views/confirmable/mailer/reset_password_instructions.html.erb
    create    app/views/confirmable/mailer/unlock_instructions.html.erb
    create    app/views/confirmable/shared
    create    app/views/confirmable/shared/_links.erb
    invoke  form_for
    create    app/views/confirmable/confirmations
    create    app/views/confirmable/confirmations/new.html.erb
    create    app/views/confirmable/passwords
    create    app/views/confirmable/passwords/edit.html.erb
    create    app/views/confirmable/passwords/new.html.erb
    create    app/views/confirmable/registrations
    create    app/views/confirmable/registrations/edit.html.erb
    create    app/views/confirmable/registrations/new.html.erb
    create    app/views/confirmable/sessions
    create    app/views/confirmable/sessions/new.html.erb
    create    app/views/confirmable/unlocks
    create    app/views/confirmable/unlocks/new.html.erb 
You'll then be able to access these files directly in your project to style them like your application.  You'll also be able to change the messaging in the emails Devise sends out through the generated mailer views.  
Last, don't forget to add config.action_mailer.delivery_method and config.action_mailer.smtp_settings in your app/config/environments/{environment_name}.rb file.  This is what my production.rb file looks like:
  config.action_mailer.delivery_method = :smtp
  config.action_mailer.smtp_settings = {
    :address              => "smtp.gmail.com",
    :port                 => 587,
    :domain               => '[redacted]',
    :user_name            => '[redacted]',
    :password             => '[redacted]',
    :authentication       => 'plain',
    :enable_starttls_auto => true  }