He has insane DPS potential just slide and track the enemy
Start the fight with your 2 then as you lower their HP on the basis of HP deleted the 2 will do burst damage insane to finish off your enemy
You can also put 2 on a Enemy with lower hp and it would still burst according to the HP% of the enemy
1 has not much to do just use it for reload use QS
3 is Your Passive
Now for 4, Use it for escaping certain situations and to also hunt a running enemy, do not use it to engage fight
Fight-Run-Fortitude Heal, then fight again
Also don't forget to slide your are difficult to track and also gain 30% bullet and spirit resist during slide
Have Fun!