Once there was a powerful demon named Mahishasura. By worshipping Lord Shiva, he got the power of eternity, which means he became immortal and cannot be killed by any means. Because of this boon he started killing people. Goddess Durga was born to kill this demon Mahishasura. Lord Brahma, Vishnu and Shiva created a shakthi by using their powers and gave it Goddess Durga. Goddess Durga fought with demon Mahishasura for nine days and killed him on the tenth day. The battle between them is the symbolic of the nine days of Navratri.
Before killing Ravana, Lord Rama worshipped Goddess Durga for nine days to gain her power. Lord Rama worshipped nine forms of Goddess Durga. On the tenth day Lord Rama killed Ravana.
King Daksha’s daughter Uma was married to Lord Shiva. The marriage was against Daksha’s will. One day he performed a Yagna invited all the Gods except Lord Shiva and spoke ill about Lord Shiva. Uma could not bear the insult and jumped into the fire. Hence she got her as Sati. She married Lord Shiva after she was reborn. She stayed in her parents’ house for nine days which are known as Navratri.
Navratri falls in lunar month Ashwin during Sharad Ritu of Hindu calendar. According to English calendar it falls in the month of September/October. It is celebrated throughout the country and Nepal.
Navratri is celebrated for nine days and in different styles depending upon the region. Devotees do fasting for all the nine day and worship Goddess in different forms. Navratri is known as Navratras or Naratey in Punjab. They treat young girls as Goddess and wash their feet ceremonially, worship them and offer food. In Western India, Navratri is celebrated with the dance forms like Garba and Dandiya-Raas. In Tamil Nadu it is called golu, where people prepare steps and places idols on that. In Karnataka and Andhra Pradesh Ayudha Puja is performed. In Telangana Bhathukuamma is celebrated.