Oh, ok ... your reply seemed a bit of "why you wasting time on that crap"
5-man dungeons...yeah, there's like 7 or 8 dungeons? 2 require some rep grinding to get into them.
There's Mythic+ now for dungeons. Which is a bit like Greater Rifts in D3 but for wow dungeons. Example: do a Mythic dungeon, get a key for Mythic+2 of <insert dungeon name here>. Do the dungeon for that key, and if you finish it in time (there's a timer), you get a + key based on your time. (can be +3 or +5)
Also, next patch brings Kara as a 5man dungeon. Or rather a 5-man raid (weekly lockout!)
I played mostly casual and don't even do dungeons that often, but cdhybrid is active on the wow thread from what i've seen so he probably can explain better.