Use the Cenarion Moondust on the Moonkin Stone of Auberdine to bring forth Lunaclaw. From there, you must face Lunaclaw and earn the strength of body and heart it possesses. Speak with Mathrengyl Bearwalker in Darnassus when you are done.
Directly east of Auberdine lay many moonkin caves. The one closest to Auberdine has a Moonkin Stone inside it. Lunaclaw, the defender of the stone, will face you only when Cenarion Moondust is applied to it. Lunaclaw possesses within it a strength that you must use as one of the Claw.
You've earned the right to use this Cenarion Moondust, [player]... now show me that you've earned the right to possess the strength of body and the strength of heart needed as a druid!