What you do is you hover over the weapon (make sure it's not locked) and then hold square (or x if you're on xbox) until you see an exotic shard appear..... ......in all seriousness though, check this out : https://www.youtube.com/shared?ci=LUN6uFGJvMs That's just one of many guides on how to use it, but it's something to start you off. I do recommend learning some basics of sniping in destiny first though, like aiming at head level, strafe aiming / drag scoping and positioning before practicing with nlb because it is often more punishing than other snipers if you miss your headshots.