The tarpan or arghya , are offered to ancestors, every new-moon day. Similarly, ashraddh is performed every year on the death anniversary of the dead relative. However, the shraddh performed during pitru paksha has a special effect. Lord yama, had ordained that the offerings made during pitru paksha should reach the souls of the ancestors immediately and directly.
The pitru paksha shraddh is performed for all dead ancestors. The offerings are said to reach all the dead relatives of the person who performs the rites. Tarpana offered on the last day of the pitru paksha reach even those who died without having any children. Even those who did not offer food to the poor in their life time and those who did not perform any acts of charity and were thus denied any comfort in the pitru lok (house of the dead), receive benefits from the shraddh performed during pitru paksha. Also those whose date of death is not known and thus for whom the yearly shraddh cannot be performed, receive oblations offered during pitru paksh. Further, those who died a violent death also benefit from oblations offered during this fortnight.
On the day of the shraddh, the souls of dead relatives are invoked. According to matsya puran, these souls are identified with vasu, rudra and adityas who are the shraddh deities. the food offered to the Brahmins on the day of the shraddh and the oblations offered to the sacrificial fire by uttering the name and gotra (clan name) of the dead relative, is transformed by the power of the mantras (sacred hymns) into food appropriate for their present bodies. agni, vasus and the rudras act as celestial messengers and take this food to the respective souls. The ancestors then bless the performer of the shraddh with health, wealth and prosperity.
What customs should one observe during pitru paksha?
The person performing the rites of pitru paksha should take bath three times a day. He should observe a partial fast and take only one meal during the day. He should not shave; cut his hair or nails during the fortnight.