How do you send push notification to the selected user by using clock and NotificationStyle extension or other free extensions?

> I would like to make simple app in which when load is ready I've to be able select driver and when I click send button, selected driver has to get push notification even if his app is not running. Note: each driver will be his own login and password. How we can do?

Possibly send the notification message to a Server and from the Server to the drivers? How many would you need to send in one go?