Hindu body of scripts known as Smriti has total Eighteen Puranas and Garuda Purana is one of those eighteen. This Purana is regarding Life after Death and Hindus generally read this Purana or get it read by a Brahmin after death of their beloved so that he/she can attain Sadgati and Moksha (Liberation from Life Cycles). Garuda Purana is a Vaishnava Purana having 19000 Shlokas that are further divided into two more parts, a Purva Khanda (first part) and an Uttara Khanda (second part) respectively. The second half of this purana deals with the subject "Life after Death".
Garuda Purana is in the form of communication carried out between Lord Vishnu (one of the Lords of Hindu Trinity) and Garuda (King of Birds - vahan / vehicle of Lord Vishnu) wherein Lord Vishnu discloses the meaning of Life and details of Life after death, proper funeral rites and reincarnation of the departed soul if proper funeral rites have been performed at the time of Antim Sanskar (Antyesti) of the deceased.
Garuda Purana is customarily read from the 4th day of death till the 11th day, in the evening time, in the presence of all the family members. Thereafter on the 12th day, the concluding ceremonies are performed. This Purana is supposed to guide and give instructions to the soul regarding which path to follow after death, it imparts Sadgati and Moksha to our Ancestor's soul. It becomes mandatory to get it performed for the fulfillment of their wishes, happiness and peace on this Loka (Earth) and Parloka (Heavenly abodes). If proper rituals have been taken care of after their death including recitation of this Garuda Purana, the Ancestor gets rid of Life Cycle and happily graces the performer with his/her blessings.
This Puja / Homam is done individually for the person, whom the pooja has been requested.