As the tank on most of my first time dungeons, I do read up / watch up on dungeons to get a feel for them, but you don't really get the full grasp until you dive right in.

If it's your first time in the dungeon, feel free to say so and people will understand! Alternatively, if you can't type, just make sure you watch the cinematics all the way through so that people can tell who the new person is.