As the party defeats enemies, everyone involved in the battle receives Ability Points, or AP. When enough AP is collected, the character achieves a Sphere Level. This is why it is essential to switch every party member into a boss fight for at least one turn, since so much AP is at stake.
Each Sphere Level enables a character to move one node forward on the Sphere Grid, or up to four nodes backward if desired. Open the Sphere Grid and press X. After selecting the Move Command, the number of nodes you can move in any direction is highlighted. Move to the desired position and press X again, and then confirm that you would like to remain at the selected position. You can change your mind and cancel out before deciding. Moving forward is essential to activating new sphere nodes and gaining new abilities.