This is also known as Krishna Jayanthi. Krishnavatharam is one of the avatharams of Maha Vishnu. We celebrate the birthday of Krishna in the month of avani on ashtami thidhi and star rohini.
In Mahabaratha, Lord Krishna advices arjuna in the battlefield. that advice is called bagavad gita. the main idea is ‘do your duty and leave the rest to God. duty is more important that anything else. be prepared to be balanced at the time of happiness or sorrow.’
we celebrate this festival preparing sweets and savories which Lord Krishna likes. we decorate the idol or picture of Krishna , decorate the floor with kolams , we draw the footprint of lord krishna depicting his entrance into our home.. from the door to the pooja place. we sing songs in praise of lord krishna like JayaDevar’s Ashtapathi(geetha govindam) and read Bhagvad Gita
we place fruits, betel etc along with aval, butter near the idol or picture of Krishna and do pooja