Not a silly question at all :) It is a celebration of Good over Evil, Light over Darkness. In Hinduism there was an evil person that kidnapped a woman named Sita. She is rescued by Rama(Not the margarine!) in a battle of Good vs Evil. After Rama rescues Sita, their way back home was lit up by people which is now celebrated by fireworks and clay lamps being lit. Use google to get a fuller story of it :)