Question about Dragonfire Inspiration

Does it really increase EACH attack's damage? Like if i successfully hit the enemy 2 time while under the effect of a +3 Dragonfire Inspiration, does it increase my damage twice (3d6 per attack, so 6d6 total bonus damage)? And what is the duration of it? Do i use it once in the start of the combat, and it remain until the end of combat? It doesn't seem to require concentration to keep it up