The word "Hindu" doesn't exist in Vedic scriptures. It was coined by the Muslims when they were trying to refer to the people in the other side of the river Sindhu in India, but they couldn't pronounce the letter S correctly. The actual religion is called Sanatana Dharma, or "Eternal Codes for living". Many modern "Hindus" don't know about it or they don't care, but our Vedic civilization is very scientific.

Sanatana Dharma was polluted in course of time, and now people have no idea about anything, they just donate laddus or pray for some material profit, like you. That is due to lack of spiritual knowledge.

Bhagavad-gita is the summary of entire Vedic knowledge or Sanatana Dharma. It says that the identity of a person is different than his/her body. The real identity of anyone is the soul, a minute spiritual spark inside the body that is eternal and doesn't die when the body dies. Such soul is present in every living entity, be it plants, animals or humans. So when a person dies, according only the body is changed, just like we change clothes when its worn out. Kinda like "deha ra aatma" poem in Class 9 or something.

Specially Chapter 2 Verse 13 says:

"As the embodied soul continuously passes, in this body, from boyhood to
youth to old age, the soul similarly passes into another body at death. A
sober person is not bewildered by such a change."

Source: http://vedabase.net/bg/2/13/en

Krishna further explains the nature of the soul in verses 20 and 24

"For the soul there is neither birth nor death at any time. He has not
come into being, does not come into being, and will not come into being.
He is unborn, eternal, ever-existing and primeval. He is not slain when
the body is slain."

"This individual soul is unbreakable and insoluble, and can be neither
burned nor dried. He is everlasting, present everywhere, unchangeable,
immovable and eternally the same."

Source: http://vedabase.net/bg/2/24/en

Hope it helped! BTW I am not an atheist. :)