What is push notification? How it works?

Push notification is a feature to make the announcement from a given mobile app to a given device. It enables users to have a certain interest in the application in iOS and Android so that many mobile app developers consider it as a tool to reach the client. But, How it work? There are typically multiple App developer, each making one or more persistent and secure connections with Push Notification Centre. They are sending app's notification, though Push Notification Centre to thousand of devices on which their users are installed.

About supported operating systems

We provide support for and recommend using the following devices:

Android running OS and newer.

About supported; https://faq.whatsapp.com/android/download-and-installation/about-supported-android-devices