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The Apple Game Center allows you to find other people to play with, compete in challenges, and keep track of your turns in turn-based games. The Game Center comes preinstalled on all iOS devices. If you can't find the Game Center, swipe down on your screen to open the Spotlight Search, and then type "game center". When you launch Game Center for the first time, you'll be prompted to sign in with your Apple ID. This is the name that will appear in leaderboards and will be displayed to your Game Center friends. You can link your iCloud Contacts and Facebook accounts to add friends, and you can also add people you play against when playing games. Your friends will appear in the Friends tab, and challenges will appear in the Challenges tab once you have some friends that play the same games as you.
Open the Game Center app. Sign in with your Apple ID. Create a profile name. Add friends.