Errors when adding an AdMob Interstitial Swift ad

I'm trying to add an AdMob interstitial ad, but I don't know how. I tried the YouTube tutorial but I get 2 errors.

var interstitial: GADInterstitial!

  override func viewDidLoad() {
    super.viewDidLoad()

    self.interstitial = self.createAndLoadAd()

  func createAndLoadAd() -> GADInterstitial {
    var ad = GADInterstitial()
    ad.adUnitID = "myInterstitialID"

    var request = GADRequest()

    request.testDevices = ["2077ef9a63d2b398840261c8221a0c9b"]
    ad.loadRequest(request)

    return ad
}

@IBAction func adButton(sender: AnyObject) {
    if (self.interstitial.isReady)
    {
        self.interstitial.presentFromRootViewController(self)
        self.interstitial = self.createAndLoadAd()
    }
}