To become a Royale, you need to play in Royale mode and win all the matches until you are the last one standing.

After you've become a Royale you will gain access to the Royale Lounge, and its rankings and chats.

After each royale win, you will see your crown count increase by one. 

As you collect Royale wins you'll unlock crowns for your avatar :)

Good luck and get that crown!