On the tournament info page, you'll see a Register button which you can use to register yourself, you and your partner as a pair and your team (if you're team captain).
Once registered, you'll be added to the list of registered users and you'll see two other buttons, one to Cancel Registration, the other one to Join the Lobby.
Here's a quick video tutorial of how the registration works:
With version 1.3.0 we have introduced the possibility to play a tournament over the course of 24 hours.
Registration still works as explained above. You'll be directed to the table as soon as you click on the Register button.
If you want to stop playing, you can just click on the Leave button, which will allow you to leave the table while saving the status of your game.
When you're ready to start playing again, go back to the tournament page (which will now show a message saying "You are already registered for this tournament) and click on the Play button.
You'll be directed to the board you were playing before leaving the tournament.