The word Tantra is formed by the combination of two words tattva and mantra. Tattva resembles science of cosmic principles while mantra refers to the science of mystic sound. Tantra has its existence in our Indian spiritual studies since past and has a detailed description in the spiritual texts. But till now its considered to be associated for an evil use, people even consider it to be black magic.
If one looks back to its existence in our Indian society, we can trace that its broadly mentioned in the Vedic texts. This is originally an important Indian tradition which is dealt with performing pooja and worshiping deities.
The most favoured deities are Sun, Shiva, Shakti, Vishu and Ganesha. In the ritual performed the god and goddess are worshiped and honoured to please them. For this several shlokas and mantras are also recited.
There are generally 16 principal ritualistic accessories used in the ritual starting from asana(seat), swagata(welcome), Padya(water for washing feet), Arghya(rice, flower, sandal paste), Achamana(sipping water), Madhuparka(honey, ghee, milk, curd), Snana(bathing), Vasana(clothes), Abharana(gems), Gandha(perfume and sandal), Pushpa(flower), Dhupa(incense stick), Deepa(flame), Naivedhya(food) and Namaskar(prayer). These offerings can vary from god to god, but are the often followed ritual.
The key elements of Tantra are mantra and yantra, these two instruments helps to invoke the deity. Some of the ritual also includes some sacrifice to please the deity. The tantric meditates and meditates considering the head as moon, heart as sun and the genital as fire.
Another element of the trantric ritual is the role of sex, the tantric text tells that sex has three distinct and separate purposes — procreation, pleasure and liberation, thus has a unique place in tantric rituals.