New to tanking any tips are welcome

I've played mmos most of my life but I've always healed and did dps, recently got back into ffxiv after years away and my friend group needed a tank. Chose the edgy dark knight and did a few dungeons with npcs and thought I was doing ok until getting into them with randoms. MY LORD ARE PEOPLE SO MEAN... for sooo many different reasons. Cuss me out for going to unnecessary rooms for loot chests (literally at my lvl) or for not knowing mechanics even after saying its my first time. Should I be watching YouTube tutorials on every dungeon before entering? Also feels like half the time even the healer is running in ahead of me pulling groups making it frustrating to keep aggro. Whats a good amount of mobs to be pulling at a time without overwhelming everyone?

Starting to realize why role queues are always waiting on tanks because people bully them relentlessly