Govardhan Puja is observed on the second day of the Diwali festival i.e. Pratipada of Shukla Paksha of Kartik month. On this day, Govardhan Parvat is worshiped. Apart from worshiping the mountain, 56 or 108 types of dishes are made by people on this day and these dishes are offered to Lord Krishna.
This tradition has been going on since Dwapara era. Before that, Indra was also worshiped in Braj. But Lord Krishna, arguing that there is no benefit from Indra; Govardhan Parvat provides protection and food for our cows. Due to which the atmosphere is also purified. Therefore we should worship Govardhan Parvat instead of Indra. After which everyone started worshiping Govardhan Parvat after obeying Lord Shri Krishna.
Seeing the peoples worshiping Govardhan, Indra Dev got angry and started raining heavily in anger. Due to the heavy rain, the people of the village started getting into lot of trouble and these people went to Krishna God to ask for help. Lord Shri Krishna asked all the Gokul residents to walk under the patronage of Mount Govardhan. In order to protect the people of his village from the rain, Lord Krishna lifted the Govardhan Parvat with his little finger, after which the Brijwasis stood under this mountain.
Lord Krishna had kept this mountain for a week. At the same time, when Indra Dev came to know that Lord Krishna is the form of Lord Vishnu, he realized his mistake and he stopped the rain. After the rain stopped, Lord Krishna places the mountain down and he says the people of Braj to observe Govardhan Puja every year, after which this festival started being celebrated every year.
On this day many people do Parikrama around Govardhan Parvat located near Mathura Vrindavan Uttar Pradesh. Parikrama has a lot of importance in Hinduism. This Parikrama has more importance than worship at home.
This day is especially important for the worship of cow. In Hinduism cow is considered as mother. This day gives the message that our life depends on everything in nature like trees, plants, animals, birds and mountains etc. That is why we need to save them all.