Also, you can register even if your team is not quite ready. So long as your team is ready by the time you want to do your first battle you are ok. The actual tournament isn't until next week (beginning on July 11th). Once your team is ready, they must be in the Battle Box on your PC. At the start of your participation the Battle Box will be locked and you will not be able to move the pokémon out until the tournament is over or you cancel your participation.
I wrote an article about the pokémon I had chosen to use in this tournament. If you want to see what I am doing to get ideas take a look.