Once the Rookie Showcase is finished, you are shown the locker room and three General Managers willing to take a risk on you in the nba, following your performance. You are given a series of questions to determine your suitability for each of the GMs' franchises, and while it may seem like they are vetting you for their own goals, you effectively decide on who signs you by answering the questions badly of teams you don't want to be drafted by. Once you've finished the questions, you're thrown into the shallow-end. Don't expect to be starting every game, regardless of who you've signed for.
TIP: You should be prepared, during your player's first year, to only Experience a limited amount of play time. This is just how the game eases you into the career mode and tries to make it a bit more realistic. Don't be fazed if you are struggling to get much time on the board, just be patient as the game will reward you for it before too long.
this does not explain it for wii players