In the world of sports said sports are supported by fans. Casual fans are the fans that don't exactly follow the sport. They're the ones who don't know who the batting coach is, or who the bench coach is, or who the team drafted in the first round, but they attach themselves to a team and cheer for the team. The die hard fans on the other hand is the fan who eats, drinks, and sleeps the team. They know every level of the team almost as much the executives of the team. They stay up as late as they have to while watching their team play on the West coast. There are even die hard fans who get the team permanently tattooed on their bodies. Die hard fans are the "crazies" who paint their bodies in team colors while it's 10 degrees in Green Bay, Wisconsin or in Ohio watching the Buckeyes.
Here's a little advice to all the casual fans out there: don't try to argue with die hard fans, they know things you don't. They know what you don't. You read the sports tabloids and think the biased gas bags of newspapers know, but the die hard fan reads things from other sources. Team insiders that know more than the gas bags. I've stopped reading sports sections years ago because I got better information from the actual team's Twitter feed or the team's blog. Casual fans usually don't read these. So when a die hard fan tells you something just listen, because you may actually learn something.
The road to becoming a fan starts with loving the sport first. If you don't love the sport then there's more of a chance that you won't understand the overall rules and regulations of the sport itself. Next look at teams from your local area to teams in other cities and combine that with the track record of success (because who really wants to cheer for losers except if you're a Cubs fan, but that's a different story), history of the teams (whether they have been a historic franchise ie. the Red Sox and/or Yankees, Los Angeles Lakers, Chicago Bulls, or the Green Bay Packers), the context of the stadium they play in (whether it be Wrigley Field in Chicago, Fenway Park in Boston, or the old Yankee Stadium).
Once you have chosen your team for whatever reason you chose then you have to decide how deep of a fan you wanna be. You can be a casual fan and watch the game whenever it is on TV or you can be a die hard fan who buys TV packages to watch their team if they don't play in your local area. The more invested you become in your team the more pride and disaster you feel with every win or loss. The ultimate feeling is when your team wins that title it's almost like you were a part of the team except that you don't get to kiss the trophy.