Lilfoot...you'll first need to create your own 'license' on the game if you haven't already. The game will assign you a 12 digit code which is unique and will appear on your license. That's your identifier for online (WiFi) play.
Go to the Mario Kart Channel on the main menu of the game, Choose Register a Friend, and enter my 12 digit code:
0473-8389-8683. You then just need to send me your code which I'll add on my system and we'll be matched up and ready to play! I'll be able to see when you're online and you can see when I'm online.
To play online we just create a room under the WFC (WiFi) menu and invite each other to come race.
Pinkyttc...gimme your code! Lets RACE!