This is a simple find-quest that will open up to part two when done.

You start the quest by locating Melithar Staghelm in the village of Aldrassil. When talking to him, he will tell you the following:

Thank goodness you are here. Strange news has traveled to me through the whispering of the forest spirits.

The mysterious woodland protector, Tarindrella, has returned to Shadowglen. The dryad's presence has not been felt in the forests of Kalimdor in years. Something is surely amiss if she had journeyed back to this land. Seek out Tarindrella and see what business she tends to in our grove. One of the Sentinels reported seeing her to the west of Aldrassil. So, simply go search for Tarindrella.

She is easily located just south-west of Aldrassil. When you find her, speak to her:I see you found me, young night elf. Melithar is a wise druid to have sent you.

Complete the quest, and talk to Tarindrella for the second part of the quest.