I am a lvl 35 Imp Sniper. I know I still have fifteen levels to go before fifty, but I am very confused about endgame content such as hard mode and nightmare mode flashpoints, and black hole comms. Just in general, what you are supposed to do once you hit 50. Answer as completely or briefly as you want.
First thing to do when you hit 50 is to grab the free tionese set by completing the advanced gear quest on the mission terminal in the supplies section of the fleet. You can also grab the PvP recruit set as well from the combat training area which will give you relics, implants and an earpiece which you can use alongside the tionese set.
Once your geared your first step is doing some tier 1 hardmode flashpoints, these will drop a single columi piece at the end as well as an odd exotech piece (which is columi without set bonus) throughout. The aim is to gear yourself up to columi so you can progress onto the next level of content as well as learning things like basic mechanics, being careful around mobs and how to work well in a group. Make you you grab the galactic conflict quests to get your columi comms which will help you gear yourself faster, also the group finder daily also gives you 5 black hole comms which you can use to buy the second best tiered gear in the game.
Once you can work well in a 4 man (you can still be tionesed geared), you can try the two story mode operations in group finder which each reward 10 BH comms and 30 columi comms but can only be done once a week each.
Once you're geared up to mostly columi, you can put your skills to the test by trying the tier 2 lost island HM flashpoint. Make sure you look up tactics before stepping in as it can be unforgiving, it is a step up from the other flashpoints. This will drop a rakata chestpiece at the end as well as tied to the rakghoul weekly quest which will reward you with 8 BH comms when you complete this alongside Kaon.
You can also progress onto the harder operations, you can do EV/KP in hardmode or you can to explosive conflict or terror from beyond story modes which each boss drops at least rakata as well as having weekly quests for getting past the second bosses in these.
From there the next stage of progression is EC HM > TFB HM > EC NiM but you'll probably need a guild to accept you on a run before you can progress onto these.