-Worldwide lets you race against people all over the world (funny how that works huh
)
-Regional lets you race people in your region. IE-Europe, US, Japan, ect
-Rivals lets you race people w/ your skill level. Not quite sure how it works, but I'm guessing it's based off your win/loss record.
-Friends lets you race people off your friend code list. Of course, they have to be online, and you both have to be searching for friends. Also in your friends list, there is a little padlock next to the name. If the padlock is 'locked' you have a better chance of connecting w/ that person.
-RF