Naga Panchami (Sanskrit: नाग पंचमी) is a traditional worship of snakes or serpents observed by Hindus throughout India, Nepal and other countries where Hindu adherents live.

Nag Panchami is celebrated on the Shukla Paksha Panchami during Shravan month. The day falls on the fifth day of the moon’s waning in the Lunar Hindu month of Shravan / monsoon – July /August.

Agricultural significance
Shravan / monsoon is the best time for cultivation in India. As fields are the dwelling ground for snakes, Nag Panchami is celebrated to calm them, so that they don’t bite them during cultivation.

The harmony and bond between human and nature

Farmers celebrate the day by not digging the fields and by worshiping snake idols made of mud.

Legends and mythology-

Lord Krishna and Kalia –

A deadly snake Kalia had been poisoning the river Yamuna and it had become difficult for the residents of Braj to drink any water. Krishna, as a child Avatar of Lord Vishnu, one day on the pretext of a ball falling down in the river has a tussle with Kalia and eventually defeats him.

Snake and Lord Shiva

A snake also adorns the neck of Lord Shiva and has a lot of spiritual significance too. The three coils around Shiva is also the indication of the past, present and the future. It also signifies that the Shakti / kundalini energy finally dances around Shiva, while Shiva the omnipresent is static.

Samudra Manthan–

Lord Shiva drank all the poison that came out from the churning of the sea. However, in the whole process few drops did fell on the ground and were drunk by snakes. People pray to snakes so that they and their families are spared of their wrath and poisonous bites.

Source:

1. https://en.m.wikipedia.org/wiki/Naga_Panchami

2. https://www.google.co.in/amp/s/www.astrospeak.com/slides/why-do-we-celebrate-nag-panchami/m-lite