Open MenuScene.swift in Xcode.

Add a new import statement at the top of the file so we can use the GameKit framework:

import GameKit

Update the line that declares the MenuScene class so that our class adopts the GKGameCenterControllerDelegate protocol. This allows the Game Center screen to inform our scene when the player closes the Game Center:

class MenuScene: SKScene, GKGameCenterControllerDelegate {

We need a function that will create the leaderboard button and add it to the scene. We will call this function once the Game Center authenticates the player. Add a new function to the MenuScene class named createLeaderboardButton as shown here:

func createLeaderboardButton...