Nine different avatars of Goddess Durga are worshipped during the nine days of Navratri with each form being worshipped on a specific day.
The first form is Shailaputri, who is worshipped on the first day of the Navratri. Shailaputri, the first among the Navadurgas, is the daughter of the King of Mountains, Himalaya. Her name, Shailaputri is the portmanteau of two words-Shaila, means Mountain, and Putri, means daughter. She is depicted as riding Nandi, the bull and holding a trident in her right hand and a lotus in left hand.
In her earlier birth, she was born as the daughter of Prajapati Daksha. Her name was Sati then and she was the consort of Lord Shiva. Once Daksha organized a big yajna and invited all, except Lord Shiva. Sati expressed her desire to visit her house to participate in the yajna.
Though Lord Shiva denied permission at first but later, considering her strong desire, he allowed her to go. Upon reaching there, Sati felt insulted as there was none to take care of her. Being a devoted wife, she felt it was an insult to Lord Shiva and could not tolerate it.
Taking strong exception to it, she jumped into the yajna kunda, or the ritual pit, and reduced herself to ashes. Hearing the entire incident, Lord Shiva got infuriated and sent his Ganas to destroy the yajna place. In the next birth, she was born to Himalaya and got the name-Shailaputri. She was also known as Parvati and Hemavati.
As per Upanishad, Hemavati reduced the egotism of lords, including that of King Indra. Like in her earlier birth, in this birth too she became the consort of Lord Shiva. This first form of the Navadurgas has immense importance and power. While the first day is dedicated to her, yogis on this day concentrate on Muladhara and start their yogic meditation.