Threat is a non issue now for the most part, extremely hard to lose threat unless it is to another high vengeance tank. Knowing how to use your active mitigation, however, has tanking being more enjoyable than it has ever been. Tanking itself is engaging and about timing. I'd suggest tanking for anyone, it is a lot of fun, but I wouldn't suggest going in to things completely blind. People WILL get upset at you and WILL give you a hard time.
Start by reading the dungeon journal in game and then if you still don't feel comfortable just google something like "stormstout brewery heroic guide" or something like that. The information should be incredibly easy to find.
DO NOT, under any circumstances go into lfr as a tank and say two seconds before the pull (or as most do, wait till they wipe the group first) "never been here, don't know what to do" because you WILL have a bad time.