New to nba 2k13
is 'Virtual Currency', or VC. This is earned as Experience
the more you play the game, and is used to purchase items from the in game store. You can purchase VC using real money, or basically work yourself into the ground in MyCareer mode to grind your way to a good amount of them. In your first season in MyCareer you are unlikely to have any VC to spare, and it will be a fairly hard grind before you have enough to feel like you can spend it on what you like - if indeed you ever get to that stage.