What is push notification?

First, you have to either rent or own a server that is responsible for communicating with Apple's APNS servers. Yes, when pushing notifications to your app's users, your server have to first push it to Apple and have Apple transfer those notifications to specific users on your behalf.
And second, implement and modify the following methods in your delegate's .m file:
//implement these funtions - (void)application:(UIApplication*)application
didRegisterForRemoteNotificationsWithDeviceToken:(NSData*)deviceToken { - (void)application:(UIApplication*)application didFailToRegisterForRemoteNotificationsWithError:(NSError*)error { - (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo {
//modify this one - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions: (NSDictionary *)launchOptions {