How to create Notifications
How to create custom Notification in WordPress
Then you just have to activate it and you are all set!
In your WordPress dashboard you should see the
Notificationsmenu. It will contain the
Add New Notificationlink which will take you directly to your fresh Notification.
You can give your Notification a Title you want (for internal use only), select the Trigger you want to use and configure your Carriers.
To read more what the Trigger and Carrier is, see this article: