Visakha Puja, is an extremely important day in the Buddhist tradition, for it was on this day that the Buddha was born, and 35 years later awoke to the unexcelled right self-awakening, and another 45 years later passed away into total nibbana. In each case, these events took place on the full-moon day in May, when the moon is in the Visakha asterism, which is why the day is called Visakha Puja.
Every year when this important day comes around again, we Buddhists take the opportunity to pay homage to the Buddha as a way of expressing our gratitude for his goodness. We sacrifice our daily affairs to make merit in a skillful way by doing such things as practicing generosity, observing the precepts, and listening to the Dhamma. This is called paying homage to the virtues of the Triple Gem: the Buddha, Dhamma, and Sangha.