The Training Sphere is a simulation sphere that is primarily used to train Rookies. It helps them go over the mistakes they made in their missions. It can also make perfect simulations of Villains and battles against them.
The Training Sphere is used by Rookies to prepare them for becoming part of a team. While Rookie William Furno was on a simulation of the desert planet Fabulox 18 he was being interviewed by Hero Factory FM. This distracted him and meant he needed to restart the mission.
The Training Sphere is located directly above where Hero Factory FM is casted.