Is it possible create NSNotifications in app and then from any form (apple.com) send push notifications to apps users? How can I do it?
To push notification to users, you need a your backend environment with your certificates. You also have to receive the user device token needed to send the push notification.
Here there is a complete tutorial to make all the necessary for push notifications: http://www.raywenderlich.com/32960/apple-push-notification-services-in-ios-6-tutorial-part-1
NSNotification is another thing and is local..in your app. You can use that to generate notification in your app at certain time or when a certain event happen.