Seed and fruit
What is a seed today will become a fruit someday and a fruit will have a seed. The cycle moves on and every action has a equal and opposite reaction. We can assume from an action what would be the result.
KArma cannot be destroyed or end without a result. A man who does something will face the result of whatever he has done. The result may take different forms and takes a seat in his spirit or intellect. it travels through the indriyas.
When 5 mahabhootas combine with the Spirit life/birth takes place in the womb.
Without the doer and the reason any action or karma cannot take place. There is a reason behind everything.
Nimit or the thing which is involved in the action is important too. Without the sand and tools a potter can not make a pot.
Karma would always lead to a result. What you do you will get back. YOu will get a similar result according to the karma you have done. Good karma leads to good result and bad to bad.
The seed of babool cannot grow a tree of mango. Similarly, type of karma defines the result KArma is the seed. What we grow, we shall reap.
This way by understanding the concept of rebith a person should endeavour to learn about the dharma and good karma.
One must observe brahmacharya and serve thy guru. LEarn about the vedas.
Second, one must get married and set up grahasthashram (family), kids and make sure that everyone is fed in the family. Respect the guests and treat them like God.
one should stay away from bad karmas theft, lie etc.
By living a sattvic life according to the vedas one man would reach salvation.