SWIFT

navigationcontroller.pushviewcontroller

//Appdelegate.swift

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: NSDictionary?) -> Bool {
    self.window = UIWindow(frame: UIScreen.mainScreen().bounds)

    let navigat = UINavigationController()
    let vcw = ViewController(nibName: "ViewController", bundle: nil)

    // Push the vcw  to the navigat
    navigat.pushViewController(vcw, animated: false)

    // Set the window’s root view controller
    self.window!.rootViewController = navigat

    // Present the window
    self.window!.makeKeyAndVisible()
    return true
}

//ViewController.swift

@IBAction func GoToNext(sender : AnyObject)
{
    let ViewController2 = ViewController2(nibName: "ViewController2", bundle: nil)
    self.navigationController.pushViewController(ViewController2, animated: true)
}