Build something that works
Try looking at this article from the Devise wiki: https://github.com/plataformatec/devise/wiki/How-To:-Add-:confirmable-to-Users
Keep in mind that in addition to the steps listed there, you'll also need to set up your app to be able to send email. There are a few different services you can use, but one of the simplest is Gmail. See more details here: https://baserails.com/questions/50.