Brave It’s much simpler to use than it was in MHW. Basically you have three “songs”. To play a song, you have to first queue up the notes - one song is played with X, X, one is A, A, and one is X+A, X+A. So you queue up the notes naturally by whacking the monsters. Then you press perform (RT) - that consumes the notes you’ve queued up, plays the songs, triggers an attack and gives everyone a buff. You can queue the notes in any order and play any or all of the songs at a time. That’s pretty much it. There’s a new thing where if you have all three songs queued up and you press RT+X you get an extra buff/attack.
Aside from that, it’s a big blunt weapon so you generally want to go for the head. It has a nice long reach and feels really mobile (well, to me, coming from lance). It’s loads of fun, give it a try. I would imagine there’ll be a decent amount of crossover for you from having already played hammer.