Tournaments on MyGameBooking come in three shapes: a league, where everyone plays everyone; a knockout, where one loss sends you home; and groups followed by a knockout, which is the World Cup shape. The listing says which, along with the team limit, the entry fee and when entries close.
Enter early. Spots are limited and the count on the listing is live, so a tournament that shows three spots left on Monday can be full by Tuesday. Your entry is confirmed the moment the fee goes through, and the fixture list comes from the organiser once entries close.
On the day, arrive before your first fixture with the squad you registered. The organiser has your entry on their desk, so there is nothing to print — just play.