Hello mut,

"How does it work?
You enter any tournament simply by entering the appropriate room ("Tournament Room") during the tournament period. No registration is required, you can enter the room at any time.

FlyOrDie Tournaments are rating tournaments. There are two types of tournaments:

Challenge mode: you play whoever you want, just like in normal play.
Automatic mode: the system makes the pairings, trying to find the most suitable opponent for everyone."

Tournament Rules:  

https://www.flyordie.com/games/help/tournamentModeration.html