The Notification plugin can be downloaded from official WordPress repository. That means you can search for it in your WordPress dashboard.
Then you just have to activate it and you are all set!
In your WordPress dashboard you should see the
Notifications menu. It will contain the
Add New Notification link 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: