Diwali is a holiday celebrated by belivers of Hinduism, Shikism, Buddism and Jainsim. It is the celebration on the day of Kali Puja. It is started by the incarnation of Lord Vishnu who was Ram at this time. He was the current ruler of Ayodha and it is celebrated because on the day of Dussehra, he killed the demon named Ravan who had taken Ram's wife, Sita. Ram worked with Laxman (Ram's brother) and Hanuman who was the incarnation of Lord Shiva and a devotee of Ram. Ram fights with Ravan in that day and finishes the last demon of Treta Yuga.
He later returned to his kingdom of Ayodha. That day, Ayodha was happy and celebration with fireworks and lighting up their house. Through this day this is the celebration that has been celebrated all around India with fireworks and lightening.