When it comes to sending a file you can find all information in here http://api.rubyonrails.org/classes/ActionController/Streaming.html There are most important cuts:
Simple download:
send_file '/path/to.zip'
Show a JPEG in the browser:
send_file '/path/to.jpeg', :type => 'image/jpeg', :disposition => 'inline'
Show a 404 page in the browser:
send_file '/path/to/404.html', :type => 'text/html; charset=utf-8', :status => 404
to use one of this option you have to create a new action in controller like this:
class SomeController < ApplicationController
def download_file
send_file image.attachment.path
end
end