Fill the Jade Phial and bring it back to Corithras Moonrage in Dolanaar.
First, let me tell you more of the task you must complete. The druids in Darnassus use the water of the moonwells of Teldrassil, and their moonwell must be replenished from time to time. Using these specially crafted phials, you can collect the water of the moonwells.
Take this vessel to the moonwell outside of Starbreeze Village to the east, and fill it with some of its waters, then return to me. When you have completed your task, I shall continue the story where Tenaron left off...