Wolves use howling as a tool to talk to their pack.
The presence of the moon when a wolf howls, as it turns out, is purely coincidental and circumstantial.
“Many ancient civilizations stretching back to the Neolithic Age continually paired wolves with the moon in images and literature, which eventually evolved into today's popular belief,”.
Since the full moon offers more light for the wolves to see by, and the fact that wolves are a nocturnal animal by nature, their howls are simply a part of their being more active on more brightly-lit nights.