Create a new CocoaTouch Class SecondViewController, subclassing UIViewController including XIB and create IBOutlet for the label
Declare a variable:
var labelTitle: String! in SecondViewController
SecondViewController ViewDidLoad will look like this:
override func viewDidLoad() {
            super.viewDidLoad()
            titleLabel.text = labelTitle
}
// Whereas titleLabel is the UILabel Outlet connected from XIB
Now in your FirstViewController, on your button Tapped action
add the following
@IBAction func buttonAction(sender : UIButton) {
    // If the VCs are in a storyboard you will need to get the storyboard to access them
    let mainStoryboard = UIStoryboard(name: "Main", bundle: nil) as UIStoryboard
    let secondVC = mainStoryboard.instantiateViewControllerWithIdentifier("SecondViewController") as! SecondViewController
    secondVC.labelTitle = sender.titleLabel?.text
    // If not do this
    let secondVC = SecondViewController.init(nibName: "SecondViewController", bundle: nil)
    secondVC.labelTitle = sender.titleLabel?.text
}
//Next present or push your ViewController