Dussehra is celebrated because it is believed that on this day lord Rama defeated Ravana. It is celebrated on the tenth day of Navratri. On Dussehra we burn huge effigies of Ravana, his son Meghnath and his brother Kumkaran, by a fire arrow.
People buy new clothes to wear on this occasion. People go to fairs which are set up in open fields on Dussehra. In the fairs there are stalls of tasty dishes for people to buy and eat. There are also stalls for souvenirs.
Dussehra teaches us to be good like Rama and not to be overpowered by our achievements like Ravana, which led to his death.
On Dussehra most people burn green crackers which produce less pollution than regular crackers. At that time children have holidays, so they enjoy their time with their relatives. On Dussehra, people get together with their families. Some people donate things to the poor people to help them also enjoy this festival time.
For me, Dussehra is a time to improve on my bad habits and strive to be a setter human being. We do not kill but conquer, the Ravana inside us!