How is it possible to send a notification programmatically, when the App got completely closed? 

Example: The User closed the App, also in the Android Taskmanager, and waits. The App should send a notification after X Seconds or when the App check for Updates.

I tried to work with these code examples but:

* [Pushing notifications when app is closed](https://stackoverflow.com/questions/37906371/pushing-notifications-when-app-is-closed) - too many Activities/doesn't work
* [How do I get my app to send a notification when it is closed?](https://stackoverflow.com/questions/24002188/how-do-i-get-my-app-to-send-a-notification-when-it-is-closed) - much information, but I don't know how to deal with it
* [How to send local notification android when app is closed?](https://stackoverflow.com/questions/24327453/how-to-send-local-notification-android-when-app-is-closed) - much information, but I don't know how to deal with it

If you can, try to explain it at an example, because beginners (like me) can easier learn it this way.