According to Blizzard, the initial raid content is going to be split up into three mini-tiers, with Mogu'shan Vaults being the first of these tiers:
1. Mogu'shan Vaults
Open one week after launch for normal raiders, the main adversary is the Will of the Emperor, which is less of a boss than an event, as described by Ion Hazzikostas, lead encounter designer:
The core chamber of the Vaults contains an army of terracotta warriors that are built into recesses within the walls. If players look up, they’ll see these statue-filled niches stretching above them into the distance. When the players enter, the statues begin animating and attacking in huge waves, and the fight quickly turns into a free-for-all. There will be certain heavy-hitting statues that require tanking, and many of the other statues have special abilities to keep the non-tanks busy. It’s going to be a crazy fight that requires lots of crowd control.
The next two mini-tiers are reportedly the Heart of Fear and the Terrace of Endless Spring, which correspond to two parts of the same narrative:
2. Heart of Fear
Open four weeks after Mogu'shan Vaults for normal raiders, the main adversary is Grand Empress Shek'zeer, who:
has been possessed by the Sha of Fear
3. Terrace of Endless Spring
Open for normal raiders once they complete the Heart of Fear, the main adversary is the Sha of Fear, who:
has escaped the Heart of Fear once Grand Empress Shek'zeer was defeated.
As of the time of answering, Blizzard has revealed one source of the Elite gear:
These items are obtained by defeating Protector Kaolan last on the Protectors of the Endless encounter.
(Source)
From this, it would appear that Blizzard is moving to, at least in some encounters, adding Ulduar-style "dial your own difficulty" encounters for Mists raids, and compensating raiders that complete the hardest version with a half-tier improved gear.
Best Answer
Mogu'shan Vaults is located in the north east of Kun-Lai Summit, on the Mogu'shan Terrace, overlooking the Zouchin Province at the foot of the mountain.
This instance has its own summoning stone just outside the instance entrance, it appears that other than summoning this instance requires wisdom of the four winds to access the instance.