You can always follow up with this Xamarin tutorial on the basics on how to implement push notifications on iOS:
https://developer.xamarin.com/guides/ios/application_fundamentals/notifications/remote_notifications_in_ios/
Besides that the GitHub documentation implies this:
Call CrossPushNotification.Current from any project or PCL to gain access to APIs.
Must initialize plugin on each platform before use. If not initializated before using a method (Register/Unregister) will thow PushNotificationNotInitializedException.
CrossPushNotification.Initialize<'T'> This methods initializes push notification plugin. The generic T should be a class that implements IPushNotificationListener. This will be the class were you would listen to all push notifications events.
iOS On the AppDelegate:
public override bool FinishedLaunching (UIApplication app, NSDictionary options)
{
//Consider inizializing before application initialization, if using any CrossPushNotification method during application initialization.
CrossPushNotification.Initialize<CrossPushNotificationListener> ();
//...
return base.FinishedLaunching (app, options);
}
And I guess that you've already implement the IPushNotificationListener
Beside that you will need to Register/Unregister the device when needed, So I think the plugin is pretty self explained.
There is a similar thread on this topic related to this:
How to use Push Notifications in Xamarin Forms
Hope this helps!