The human being is a blend & coexistence of the conscious soul and the physical body. Death is destined the moment birth happens. When the soul adopts a body in the womb, birth happens. When the mother pushes the baby out into the world, experiencing begins. Similarly when the soul leaves the body death happens.
The body is a physical substance in which integration and disintegration is going to be always happening. The soul energises and instructs the body to function and once that bond is broken the body becomes lifeless. The soul is never changing and will adopt another body to experience bliss again.
Matter is in a continuous state of formation and disintegration and this keeps going on. The body which is made up of physical elements will be decomposed and blended with the matter and go into a recycling process.
The soul which is immortal and is complete continues its quest to find another body and finding enlightenment. Soul understands and experiences things in life. It is what is the root cause for all the activities performed by the physical body.
To understand more in detail you can validate with the actual deaths taking around you and understand the same. The soul can be understood by studying your own-self and knowing what is the existential reality.