Kali Puja is performed on night of Kartik Amavasya in the Hindu month of Ashwin according to the Bengali calendar, the same night when the rest of the world celebrates Diwali. Though mostly celebrated in the states of West Bengal, Orissa, and Assam; it is celebrated in other parts of the country as well. Kali Puja was practically unknown before the 18th century, however a late 17th century devotional text Kalika mangalkavya –by Balram mentioned an annual festival dedicated to Kali. It's believed that Maharaja Krishnachandra of Navadvipa started the first of the ritual. The puja is usually it is done in Brahmanical form but there is a more virulent Tantric form of this puja in which She is offered animal blood in a skull, sweets, rice, lentils, fish and even meat. Animal sacrifice used to be a part and parcel of this system but it is gradually fading away.
The Goddess in Kali avatar has four arms. She holds in one a weapon, in another the head of an asura or demon, dripping blood; the other two are raised to bless the worshipers. Her body is covered with her 'ornaments', which include necklace of snakes, skulls and heads of demons and a belt from which hangs demon's hands, which signify Karma or action. Her tongue hangs out with blood in it, blood of Raktaveera, a demon who managed a boon from Lord Bramha that every drop of blood which fell from his body would be able to produce thousands more like him. Kali developed her thirst for blood after killing the demon Raktavera and drinking her blood!
Despite her fearful appearance, the relationship that devotes share with her is that of a loving and caring mother. She is considered the deity of time and eternity and worshipping her lightens up the darkness of ignorance and ‘maya’, or lust for worldly possessions, within the devotees. Moreover, with her eternal blessings, all the sorrow, misfortunes, and sufferings are healed. Dakshineshwar Temple and Kalighat Temple in Kolkata, and Kamakhya Temple in Assam are dedicated to Goddess Kali and visited by thousands of devotees every day. Swami Vivekananda’s Guru, Thakur Ramkrishna Paramhansa Dev remains the most celebrated devotee of Goddess Kali.