Ok, so as i was merrily leveling my sholar and warrior (37 and 36 currently) one thought can't leave me alone. What's with all those difficulty levels and how do they size up to eachother?

Right now i just have normal mode dungeons, so ok, that's simple. Hard mode unlocks at lvl 50. Ok no brainer here. But then i here something about EX difficulty and "savage" raid or something?

So how do these two rank vs eachother and hard mode and are there any special quirks regarding them, asides of being hard?