Very simple methods Just go to the terminal and the type following
rails g devise:controllers users //This will create devise controllers in controllers/users folder
Next to use custom views
rails g devise:views users //This will create devise views in views/users folder
now in your route.rb file
devise_for :users, controllers: {
:sessions => "users/sessions",
:registrations => "users/registrations" }
You can add other controllers too. This will make devise to use controllers in users folder and views in users folder.
Now you can customize your views as your desire and add your logic to controllers in controllers/users folder. Enjoy !