Sky burial is simply the disposal of a corpse to be devoured by vultures. In Tibetan Buddhism, sky burial is believed to represent their wishes to go to heaven. It is the most widespread way for commoners to deal with the dead in Tibet.

If a Tibetan dies, the corpse is wrapped in white Tibetan cloth and placed in a corner of the house for three or five days, during which monks or lamas are asked to read the scripture aloud so that the souls can be released from purgatory. The Family members stop other activities in order to create a peaceful environment to allow convenient passage for ascension of souls into heaven.

Later, the Family members will choose a lucky day and ask the body carrier to carry the body away to the celestial burial platform. On the day before the burial, the family members take off the clothes of the dead and fix the corpse in a fetal position. Specifically, the body is bent into a sitting position, with the head against the knees. At dawn on the lucky day, the corpse is sent to the burial site among mountains which is always far from the residential area. Then 'Su” smoke is burned to attract condors, Lamas chant sutras to redeem the sins of the soul, and a professional celestial burial master deals with the body.

Practice of sky burial is closely related to philosophy of Tibetan Buddhism. Tibetans believe that if the vultures come and eat the body, it means that the dead has no sin and that his or her soul has gone peacefully to the Paradise. And the condors on the mountains around the celestial burial platform are 'holy birds' and only eat the human body without attacking any small animals nearby. Any remains left by the holy birds must be collected up and burnt while the Lamas chant sutras to redeem the sins of the dead, because the remains would tie the spirits to this life.

Source : http://.tibettravel.org/tibetan-local-customs/tibetan-funeral.html