After Meet with Mylune, Join the Dreamer wants you to find Naralax. The entrance to find him underground is at [47, 30] in the Dreamgrove. It's labeled on the map with "Tel'Andu Barrow Den" with a picture of an entrance. That's where the tanking quest chain takes you too, to find Lea Stonepaw in Mistress of the Claw.
The next quest in this chain is In Deep Slumber. Walk onto the rugs behind Naralax, and drink the [id=135506] in your bags that he gives. I'd suggest using your prowl ability to sneak back out of Tel'Andu Barrow Den. You have to avoid any of the red water and the red ooze trails on the ground or it will cause corruption, wake you from the dream, and you'll need to drink from the cup again. You can prowl in cat form to avoid combat entirely, or kill creatures as needed. The ramp out of the den is blocked with vines, but you can hop up the edge of the ramp near the vines (it will take a few tries). If your red corruption meter in the center lower part of your screen is nearly full, heal yourself to lower the corruption. Once you're out of the Den, you just head to [45, 51] to complete the quest, then you'll be teleported out of the dream back to Naralax.
The quest after that is Reconvene, you just go back out of the Den to [45, 52].
The next quest is Cleansing the Mother Tree. The quest marker shows coordinates [55, 22], a big swirling portal in the Dreamgrove. Go through that to go from the Dreamgrove to the Emerald Dreamway. Within the Emerald Dreamway, take the easternmost portal, to Mount Hyjal, located at [53, 53]. You'll teleport into a scenario.
In the scenario, heal the friendly targets marked on your minimap, and cleanse [npc=104658] with your Nature's Purge spell. Talk to [npc=104658] to tell her you're ready. Soon the other NPCs will join your party, and you have to keep everyone healed through the battle. In stage 5, just heal everyone up, and click [npc=104628] at [60.5, 25.5] to give her the G'Hanir staff. In stage 6, click the staff to wield it. In the final stage, click your extra action button to call the creatures of the forest to kill [npc=104686]. IMPORTANT: If you don't have an extra action button in the lower middle of the screen, type: /click ExtraActionButton1
Once combat ends, go back through the Dreamway portal at [59, 26], then back through the Dreamgrove portal at [45, 25], then turn in Cleansing the Mother Tree at [45, 52] to finish the quest chain.