Before you get started
Make sure you update to the most recent version of the software.

Add a friend
Find your friends in Game Center to share your achievements, high scores, and more.

On your iPhone or iPad

  1. Open Settings, scroll to Game Center, then tap it.
  2. Tap Invite Friends.
  3. Search for the person you want to invite, or look through the list of suggestions.
  4. Tap Invite next to the person's name.
  5. Game Center sends an invitation notification to their devices. If they have the Messages icon next to their photo, they're on a previous version of the software and you can send them an invitation in Messages.

On an iPhone, the list of people someone can invite is showing. In the bottom left of their photo, they have a Messages icon. To the left, it says "Invite".

Note: you must have the person in your Contacts already!

Accept a friend request
To accept a notification invitation, tap or click it, then select Accept. If you tap or click Ignore, the notification will disappear and the user who sent it won't be alerted that you ignored it.

 

If you need more details, check Apple's Support Guide here