gistfile1.rb

## app/controllers/admin/users_controller.rb
def export_to_csv
  @users = User.all
  csv_string = FasterCSV.generate(:force_quotes => true) do |out|
    out << ['Email Address', 'First Name', 'Last Name', 'Mobile Phone', 'Gender']
    @users.each do |u|
      out << [u.email, u.first_name, u.last_name, u.phone_number, u.gender]
    end
  end
  send_data(csv_string,
    :type => 'text/csv; charset=utf-8; header=present',
    :filename => 'users.csv')
end

gistfile2.rhtml

<!-- app/views/admin/users/index.html.erb -->
<% form_tag({ :action =>  :export_to_csv })do -%> 
  <p>
     <%= submit_tag "Export To CSV" -%>
  </p>
<% end -%>

gistfile3.rb

## config/environment.rb
config.gem "fastercsv", :version => "1.5.0"