Lankan king Ravana, who had set eyes on Sita, had planned to take her captive, and he used Mareesa to take the form of a deer, and lured Sita, and got her caught, and abducted her to Lanka. It was after a struggle by Lord Hanuman that Lord Rama came to know of the whereabouts of Sita, and Hanuman had personally met Sita after lots of struggles. and what followed later was a huge battle between the ten-headed demon king Ravana, and Lord Rama, who was an incarnation of Lord Vishnu, one of his ten avatars.
In the battle that ensued, Lord Rama had defeated Ravana, and got back Sita, and returned to Ayodhya, and this victory of Rama over Ravana, is being celebrated by many people of India as the Dussehra festival, and they celebrate by burning effigies of Ravana.