Okay, this is what you do. You can start doing it already at lvl 68 as that is when you can take the quest from the guy outside of krazhan, in Deadwind Pass:
He will ask you to go down two cellars and touch some water. This is pretty hard so you should group up with one or two other players to be sure to make it.
After this, go to Shattrath, to a guy in the center next to the Sha'tar there.
Then it is Shadow Labs. Stupid and hard instance. Make sure to read up on the bosses before you do them or bring someone who knows how to defeat them!
Back to Shattrath.
Now it is the time for Arcatraz and Steamvaults, in whatever order. Steamvautls is really easy and can go for 20-30 minutes with a really good group. Arcatraz is a bit harder and many people hate it so you may have a hard time finding a group. Never doubt to ask the guild for help!
Back to Shattrath again.
Black Morass (Caverns of Time), also known as Dark Portal. This instance can be very hard as it has no time for breaks. When the event is started it just keeps going until you make it or die. Get a good group with good dps!
Back to Shattrath.
Done!