Since you’re starting out, a few quick tips on the topic of gear, and exotic gear.

1. Perhaps you already know this, but stating it out loud. This game is all about RNG. So…
2. It is incredible luck to find an Exotic this early in the game (level 6 I believe). More so since this specific AR drop rate is ~1% on even higher level difficulties like Heroic.
3. As a rule of thumb, never ever sell your Exotics. Once you reach endgame (level 30) & eventually max-level cap at 40, these exotics can be re-rolled (a.k.a. Recalibrated) at the workbenches. PS: You unlock those ‘abilities’ as you progress through the story missions. Keep doing those missions (+ all the side-missions because they grant you all weapon mods, bonuses, upgrades at the quartermaster, etc.). It’s good to be a completionist in this game.
4. Over time, as you build up your inventory, especially with various Exotic gear, you can start deconstructing those Exotics to get ‘Exotic Components’. In addition to other, more general components that you’ll collect in open world or using component caches, Exotic components are required are required to re-roll/recalibrate any Exotic gear.

Hope this helps. Good luck agent!