Hinduism prescribes elaborate rituals for the dead beginning from the day of burning the body till the 13th day when Subhasweekara or Auspiciousness in invited back Home.
These rituals are based on the belief that the Departed souls take rebirth and the Preta Sareera hovers around till the 12th Day.when the dead are respectfully moved to the ancestors, Pitrus.
It is the belief of the Hindus that one born to enjoy the fruits of actions one performs/ed; if Righteous deeds had been performed one enjoys happiness and sails through Life easily while Non Righteous acts bring in Unhappiness and misery when one lives.
In both the cases , the effects of the actions performed by one gets wiped out as one undergoes the experiences of Life.
In Hinduism the wages of Sin is Birth unlike Christianity and other Religions where the wages of Sin is death.
When one dies, the inert body , Sava is consigned to flames.
One becomes Sava when Consciousness leaves permanently, The Consciousness being an attribute of the Soul.
However the Sukshma Sareera, the body which one does not perceive, which surrounds one’s physical frame, remains.
The Physical frame made of he essence of food, Anna rasa dies.
But the Sukshma Sareera , which is the result of the actions one performs remain .
This sareera is like dust accumulated when action is performed.
This sukshma Sareera takes rebirth depending on the Nature of actions, Karma performed by the individual.
The Soul never dies.
The Sukshma Sareera enters into human wombs, they are reported to be 83 Million different types of Female genital parts( Yoni Beda), according to Hinduism.
The Womb chosen at rebirth is determined in accordance with the actions performed.
So till such time, that is the Twelfth-day from the date of death, the preta Sareeera lingers , hovers around the place of Death and around the Home.
This Preta once it is released after the twelfth day is reborn;in such cases where no karmas or the dead performed rebirth still takes place;in this case the Reborn, in the new Life will have unexplained issues facing its new Life.
This is Pitru Dosha.
Another kind of Pitru Dosha is one that accrues when one does not perform the Rites for the departed.
This results in Pitru Saapa.
The Suksma Sreera, once it leaves the Pysical frame is called Preta and this during life has been nurtured by the essence of Food.
This has been enjoyed by it through the Physical frame.
Now that one is dead, the Preta sarera can not get Food for nurturing.
As it is yet to be released, till the Twelfth day(Sapindi Karana), it suffers.
To nurture it, the Tharpana is performed with sesame Seeds and water,the former substituting food, as sesame seeds, according to Hinduism, was the first to be created as Food, Water to quench Thirst.
It is also considered necessary to indicate the Preta that it would no longer get Food or water as it lacks the physical Frame.
As the Preta is finally elevated to the level of Pitrus on the Twelfth day,prior indication is given on the tenth day by way of offering huge quantities of food, without salt to wean away the Preta from food as it is believed that it would get disgusted with the huge quantity of food offered and that too with out Salt.
During the next two days , the preta is paid respects by a Brahmin in the ceremonies.
On the 12th day Sabindi karana is performed and the preta leaves.
On the thirteenth day Gruha yagna or Subha sweeakara is performed.