Upanishads describe reincarnation (punarjanma) (see also: samsara). The Bhagavat Gita, an important Hindu script, talks extensively about the afterlife. Here, the lord Krishna says that just as a man discards his old clothes and wears new ones; similarly the soul discards the old body and takes on a new one.
In Hinduism, the belief is that the body is but a shell, the soul inside is immutable and indestructible and takes on different lives in a cycle of birth and death. The end of this cycle is called "Mukti" (Sanskrit: ) and merging finally with God is "Moksha" (Sanskrit: ) or salvation. Garuda Purana, a book solely deals with what happens to a person after death. The God of Death Yama sends his representatives to collect the soul from a person's body whenever he is due for death and they take the soul to Yama. A record of each person's timings & deeds performed by him is kept in a ledger by Yama's assistant "Chitragupta".
According to the Garuda Purana, a soul after leaving the body, travels through a very long & dark tunnel towards South. This is why an oil lamp is lit and kept beside the head of the corpse, to light the dark tunnel and allow the soul to travel comfortably. The soul, called "Atman" leaves the body and reincarnates itself according to the deeds or Karma performed by one in last birth. Re-birth would be in form of animals or other lower creatures if one performed bad Karmas and in human form in a good family with joyous lifetime if the person was good in last birth. In between the two births a human is also required to either face punishments for bad Karmas in "naraka" or hell or enjoy for the good karmas in "svarga" or heaven for good deeds.
Whenever his or her punishments or rewards are over he or she is sent back to earth, also known as "Mrityulok" or World of Death. A person is merged with the God or ultimate power when he discharges only & only good Karmas in last birth and the same is called as "Moksha" or "Nirvana", which is the ultimate goal of a true Hindu. Atma (Soul) merges into "Parmatma" or the greatest soul.According to Bhagwadgita an "Atma" or soul never dies, what dies is the body only made of five elements - Earth, Water, Fire, Air, and Sky. Soul is believed to be indestructible.None of the five elements can harm or influence it.
Hinduism through Garuda Purana also describes in detail various types of "Narkas" or Hells where a person after death is punished for his bad Karmas and dealt with accordingly. Hindus also believe in 'Karma'. 'Karma' is the accumulated sums of one's good or bad deeds. According to Hinduism the basic concept of Karma is 'As you sow, you shall reap'. So, if a person has lived a good life, they will be rewarded in the afterlife. Similarly their sum of bad deeds will be mirrored in their next life. Good 'Karma' brings good rewards and bad 'karmas' lead to bad results. There is no judgment here. People accumulate karma through their actions and even thoughts. In Bhagavad Gita when Arjuna hesitates to kill his kith and kin the lord reprimands him saying thus "Do you believe that you are the doer of the action. No. You are merely an instrument in MY hands. Do you believe that the people in front of you are living? Dear Arjuna, they are already dead. As a kshatriya (warrior) it is your duty to protect your people and land. If you fail to do your duty, then you are not adhering to dharmic principles."