Form Helpers

Rails provides a set of view helpers for forms. They are described in
the RailsGuides: Rails Form Helpers document. Many developers use an
alternative set of form helpers named SimpleForm, provided by the
SimpleForm gem. The SimpleForm helpers are more powerful, easier to use,
and offer an option for styling with Bootstrap.

The SimpleForm and Twitter Bootstrap Demo shows how the form helpers
work with Bootstrap.

In your Gemfile, you’ve already got:

gem 'simple_form', '>= 3.1.0.rc1'

You already ran $ bundle install.

You need to run a generator to install SimpleForm with a Bootstrap
option:

$ rails generate simple_form:install --bootstrap

which installs several configuration files:

config/initializers/simple_form.rb
config/initializers/simple_form_bootstrap.rb
config/locales/simple_form.en.yml
lib/templates/erb/scaffold/_form.html.erb

Here the SimpleForm gem uses the generator command to create files for
initialization and localization (language translation). SimpleForm can
be customized with settings in the initialization file.