In the Puranas many stories and legends explain the origin and significance of the festival Maha Shivaratri.
As per one legend, during the period of churning the ocean by the gods and the demons, a pot of poison (Kaal koot) emerged from the ocean. This sudden incident terrified the dev ganas and asura ganas as the poison was capable of creating mahapralaya (deluge), which can destroy the entire universe.
To save themselves and the universe they went to Lord Shiva for help. For the worlds safer existence and the survival of living beings, Shiva drank the ‘Kaal koot visha (terrible poison). But, instead of swallowing he kept it in his throat. Keeping the deadly poison in his throat made Shivas throat turn blue. Because of this great miracle Shiva is also called Neelakanta, the one who has blue throat. To rememorise the event of Shiva protecting the world with his miraculous act, we celebrate Maha Shivrathri.
Maha Shivaratri Puja Vidhi Video