What role are you?
This is just the opinion of BetrayalEU (streamer, GM and Raid leader for the guild). It is supposed to come across as kind of joke but also holds valid merit.
WHAT IT IS TO BE A TANK
If your going to tank you are required to do your homework with routes for M+, create your own and know and understand what certain mobs do in each dungeon each season. You will also need to know what mechanics are covered by yourself when tanking raid bosses. Basically as a tank you need to hold the leader qualities and do just that lead your team to victory!
WHAT IT IS TO BE A DPS
This is where I point out that your main responsibility is to use your kicks, CCs and stuns. You are required to do this as if you don't people die and healers can't heal stupid. Your also required to learn how and when to use your defensives. Again this is help the healer and the group overall so you don't fall over and have that sweet floor PoV. Also I will repeat the healer can't heal stupid.
WHAT IT IS TO BE A HEALER
Your job is to keep the numpties in the group alive. Keeping yourself alive is also top priority, by learning to rotate and use your healing CDs correctly in order to do this. Now healers can't kick as such you can aid with any other utility that the class your playing might have. This could include certain totems (Shaman) roots/snares and slows (Druid and other classes).