how do you unlock all three team assignments?

YOu can only do one team assignment at a time,
To get to level 10 in street to stadiums you have to select and complete the tasks. if you don't complete the tasks you don't get any points

You play every fame moment then you will get 10 fame points

If you meen a club, The National Team And the Classic team then you have to get to Level 10 And 11 Then go to Options and View Created players, Click your Player At the bottem Click Where it says Change club, Chose Your Leage and Club Then Click Your countrys Symbol (Only if you made it to Level 10) And add your player to the Roster Then bes that you will see the classic team symbol click that delee one of the players from the Original Roster then add your self and thats all 3. BUt you can't make your self in 3 clubs unless you Make a new player in streets to Stadiums and click use and existing player and click the player you want and repeat the first part. You get to Level 10 By Completing Fame moments That you chose before every game. I don't want to explain how you select them cause I wrote alot but if you wanna find out make a new Streets to Stadiums Player adn Actully READ the instructions :P

You can unlock the club assignment at the begginning.You need fame level 10 to unlock nationanal team assingment, and you need fame level 11 to unlock classic assingment mode