Pitru Paksha is a period of 16 days that is dedicated to the ancestors. Donations are made during this time to pay homage to one's forefathers and gratify their souls.
Shradh rituals and pooja methodologies would be more effective if it is done under the guidance of an expert Vedic astrologer.
According to Hindu mythology, the tradition of offering Shradh (donations) during Pitru Paksha is attributed to Karna. Karna was a charitable person and had donated gold and other precious things throughout his life to help the needy and downtrodden. When he died, his soul went to heaven, where he was given gold and jewels to eat. Bemused, he went to Indra to know the reason for the same. Indra told him that despite donating many things, particularly gold during his life, he had never donated any food to his ancestors. Karna reasoned that since he wasn't aware of his ancestors, he never donated anything. So Indra, allowed Karna to go back to earth to do Shraddha and seek redemption.
The Ritual of Shraddha involves the male member, usually the eldest son of a family. After taking a bath he is required to wear a ring made of kush grass. The kush grass is symbolic of benevolence and is used to invoke the ancestors. The word "Kushal Buddhi" is believed to be derived from kush. Pind Daan, the ritual of offering of rice, sesame seeds and balls made from barley flour is performed. The blessings of Lord Vishnu are then invoked using another holy grass known as darbha grass. Darbha grass is known for its unhindered growth and similarly helps to remove obstacles in one's life. Food that is specially prepared for the event is offered in memory of one's ancestors. A crow, which is considered the messenger of Yama eating the food, is considered an auspicious sign. Next, Brahmin priests are offered food after which the family members have their meal.
Reading Holy Scriptures such as Garuda Purana, Agni Purana and the stories of Nachiketa and Ganga Avataram is considered propitious during this time. However, there are certain things that should be avoided during Pitru Paksha.
1. This isn't a good time for new beginnings. Avoid starting anything new, even something seemingly as insignificant as buying and wearing new clothes, washing hair, cutting hair and even shaving are prohibited during this period, especially on the last day, i.e. Mahalaya Amavasya.
2. As per Astroogi.com astrologers, getting married, celebrating the birth of a new born, settling down in a new home, starting a new business and other such important events should be postponed or advanced so as to not to fall under the period of Pitru Paksha.
3. Eating non-vegetarian food or even including onion and garlic in the food is forbidden.
4. It is believed that only when a person performs the rituals with earnestness and no malice at heart does his efforts bear fruit. Thus, it is important to clear one's mind of all negative thoughts and pay reverence to one's ancestors with utmost sincerity and respect. It is also important to refrain from pleasurable activities for the ritual to be successful.