Here's a guide to Apple Arcade Game Center: https://support.apple.com/en-us/105022 

and here's a guide on how Family Sharing for Apple Arcade works: https://support.apple.com/en-us/108380 

 

Firstly, the easiest way to find people is to select "Challenge Friends"

> If you're on Bluetooth + the same WIFI, other players playing WHAT THE CLASH? nearby will show up in the "Challenge Friends" overview!

 

There is also a code link system in the game! 

If you want to send a code

From the main menu

> Select "Challenge Friends"

> "Create Game"

> Copy the Invite Code and send to whoever you want to play against!

 

If you get a code from someone 

From the main menu

> Select "Challenge Friends"

> "Join Game"

> Paste the Invite Code and start the match!

 

Please note: 

You need two seperate Game Center accounts to play against each other - so if you're logged in on the same account on two different devices, that won't work.