First you register to be remembered in the Airtribune database.
Then you register for an event.

Go to https://airtribune.com/.

Click "Sign In" in the upper right hand corner:

Enter your email address and password:

Click "Register new user."

Then fill out the small amount of information required.

Click Save.

You will be sent as email to the address that you provided to verify that that
is a correct email address. You need to confirm your email address by clicking
the link given in the email. You are then registered with Airtribune.

Next click All Events and choose a competition that you wish to attend. You will
be asked to fill out more extensive information (but it will be used for your
next event also - although you can edit it then).

After completing that form and clicking Register, you have registered for a new
competition and have saved your basic information at Airtribune on their servers
in Holland.