You have to have wi-fi to access it. I'm pretty sure that on the main screen, before entering the game world, there's a Wi-Fi option. If you have a Nintendo Wi-Fi connector, select that. If not, choose search for an access point.
If you want to join the tourney, just sign up. To get on wi-fi, go into any pokemon center (except the E4, I don't think you can get on there). Once you get down there, a lady will give you the Pal Pad where you register friends codes and it has yours there. To get online though, you'll need either a wireless router or a Nintendo Wi-Fi Conector.