The only techniques you can learn in X-2's BB are Overhead Volley and Corkscrew Shot. To learn a new tech you need to win the prize that corresponds with the tech; Besaid Waterfall Shot for Overhead Volley and Kilika Stairs Training for Corkscrew Shot. When you've chosen the player you want to learn the tech, they will leave your team for a short while and you must find them again in their Scout level.

And to answer the original question, you can only play BB in Chapter 5. Go to Luca and talk to the woman at the registration desk.