The B.A.N.D. system is introduced in Opus 2 during your second fight with your fourth party member. In Elmore Greatwood, you'll be given a mission to rescue the party member and scout out the area further. The B.A.N.D. tutorial is given for the second fight, activated with R1 and defaulted with Kirika as the center. This will grant several benefits, so be sure to use this often when you can; depending on the center, it will vary in abilities and buffs, as well as it is possible to quell an enraged Shining Dragon if you have it on standby.