There are three possible answers to this question.
Those who believe in a god or gods usually claim that before an individual is created, he does not exist, then he comes into being through the will of a god. He lives his life and then, according to what he believes or does during his life, he either goes to eternal heaven or eternal hell. There are others.
Humanists and scientists, who claim that the individual comes into being at conception due to natural causes, lives and then at death, ceases to exist. Buddhism does not accept either of these explanations. The first gives rise to many ethical problems.
If a good god really creates each of us, it is difficult to explain why so many people are born with the most dreadful deformities, or why so many children are miscarrieaged just before birth or are stillborn. Another problem with the theistic explanation is that it seems very unjust that a person should suffer eternal pain in hell for what he did in just 60 or 70 years on earth.
How does the mind go from one body to another?
Think of it being like radio waves. The radio waves, which are not made up of words and music but energy at different frequencies, are transmitted, travels through space, are attracted to and picked up by the receiver from where they are broadcast as words and music. It is the same with the mind. At death, mental energy travels through space, is attracted to and picked up by the fertilized egg. As the embryo grows, it centres itself in the brain from where it later "broadcasts" itself as the new personality.
Buddhism offers the most satisfactory explanation of where man came from and where he is going. Seventy years of non belief or immoral living does not deserve eternal torture. Likewise, 60 or 70 years of good living seems a
very small outlay for eternal bliss in heaven. The second explanation is better than the first and has more scientific evidence
to support it but still leaves several important questions unanswered. How can a phenomenon so amazingly complex as
consciousness develop from the simple meeting of two cells, the sperm and the egg? And now that parapsychology is a recognized
branch of science, phenomena like telepathy are increasingly difficult to fit into the materialistic model of the mind.
Buddhism offers the most satisfactory explanation of where man came from and where he is going. When we die, the mind, with all
the tendencies, preferences, abilities and characteristics that have been developed and conditioned in this life,
re-establishes itself in the fertilized egg. Thus the individual grows, is reborn and develops a personality conditioned both
by the mental characteristics that have been carried over and by the new environment. The personality will change and be
modified by conscious effort and conditioning factors like education, parental influence and society and once again at death,
re-establish itself in a new fertilized egg. This process of dying and being reborn will continue until the conditions that
cause it, craving and ignorance, cease. When they do, instead of being reborn, the mind attains a state called Nirvana and this
is the ultimate goal of Buddhism and the purpose of life. Read More