After you've completed the hot seat races in your first season in Career mode, you will be given the opportunity to sign a contract with a team in the Xtreme Dirt Tour. Simply choose a team to race on and you will be awarded this achievement.
Side Note for other future achievements - Chose a team that is 5 stars and has the higher pay out. This will give you a better car, which will help you win more races. Also, later in the game you will need a significant amount of money to finish the achievements related to starting your own team. Also, this will help get to the "Earn $50 million dollars" achievement.