Tutorial requested: Implement Push Notifications

Hey there!
Has anyone already tried to implement Push Notifications in their app using OneSignal or Pusher or another service?

I would love to see how you’ve done it with a course or tutorial or a guide… and I’m sure I’m not the only one interested in this!
For example, a perfect use case would be the implementation of the push notifications for a chat app (whatsapp like).

Thanks!