Significance
Diwali, the festival of lights, is the most celebrated Hindu festival, symbolising the victory of light over darkness and good over evil. It marks Lord Rama's return to Ayodhya after fourteen years of exile and the vanquishing of Ravana.
The night is dedicated to Goddess Lakshmi, the bestower of wealth and prosperity, invited into cleaned, illuminated homes.
Rituals
Homes are cleaned, decorated with rangoli and rows of diyas, and the Lakshmi-Ganesha puja is performed in the evening pradosh muhurat. Families exchange sweets and gifts, wear new clothes, and light lamps and fireworks. Traders begin new account books (Chopda Pujan).
How the date is fixed
Diwali is celebrated on the Amavasya (new moon) of Kartika (amanta Ashwina), with Lakshmi Puja in the pradosh (evening) period, so the puja muhurat is shown above for your location.