Dasara is the final day of celebration during the Navaratri festival. It signifies the victory of good over the evil. There are many legends related to the celebrations of navratri and one of the popular ones is that of the Goddess Durga killing the buffalo headed demon Mahishasura.
Mahishasura was a demon with the head of a buffalo. His father Rambha was a demon and his mother was a buffalo. Mahishasura acquired great powers in due course and created havoc all around by defeating the devas. When the Gods could not bear his torture, they approached the trimurthis for help. Then Brahma, Vishnu and Shiva took charge of the situation and created the Goddess Durga out of their power.
Goddess Durga was the most powerful of all the of them as she had all the powers combined of all the Gods in the world. All the Gods lent their weapons to the Goddess owning to her supremacy. Though powerful , she was extremely good looking. Mahishasura got enchanted with her beauty and proposed for marrying her. She said she would do it if he was able to defeat her in the battle. A fierce battle ensued between them which lasted for nine days and nine nights. Finally on the tenth day Goddess Durga was able to kill the demon Mahishasura. This day came to be known as Vijaya Dashami.
In these days, people celebrate the Navratri by worshipping the idols of Goddess Durga. People worship them for ten days and on the final day of Vijayadashami, after all the pujas, her idols are immersed in the nearby lakes or rivers.