If you are new to a dungeon, just let the party know and most of the time someone will explain the boss mechanics to you. You can watch videos to get the overall feel for things, but the best teacher is going to be experience. You can watch all the videos in the world on something like Titan, but you'll still feel like you did a horrible job until you've been through it a few times. Don't worry about the elitest pricks who tell you to "git gud" and to "know fite nubs", they've just forgotten that before they became experience in the fights/dungeons/trials, that they were new too.