Most people have a concept that there are indeed three parts of man, the body, mind and spirit. But what really are they and how do they interrelate?
The easiest to understand is probably the body. Our bodies have ears, eyes, limbs and so forth. They give us sensation, so they are very real to us. We are not technically these bodies however, but rather, we are the life force that runs the body. We use these bodies to perform what we are trying to do in the physical universe.
The body itself is a composite of life within the cells and the material universe. Upon body death the life within the cells extinguishes and leaves the matter part of the cell remaining. At that point the cell is dead. The life within these cells departs variably, not all at once. Hair and finger nails will continue to grow weeks long after other parts of a body have begun to decay after what we call death.
So if we look at the body as some kind of vehicle we run, which itself is made up of aggregates of life and matter, that would be a fair description. Many religions, particularly eastern religion, have this concept.
Next is the mind. It is a compositor of pictures that a person uses to look into the past and work out solutions to problems, so as to pose solutions for the future. The pictures in the mind are something like a movie roll of one frame after the other. We are dependent on it as a data storage unit.
But the mind is also more, as there are several minds, not just one. There is what is termed the analytical mind, that perfect mind which is able to give the perfect answer, without error. It is potentially without limit. Then there is the reactive mind, that mind which has accrued all the pain and misfortune in the past - the recall of the bad times, the emotional upsets, losses and negative experiences. This mind is not needed by the person but belongs to the collective life of the body cells. Arguably it has limited use by us today as a higher life-form. The reactive mind impinges upon the analytical mind to make the person do something he otherwise would not do. To demonstrate this, who has not done something they wish they had not done, knowing even at the time they were about to do it, that it was wrong? Who has said something hateful or hurtful to someone they loved knowing it would hurt themselves later? This is the reactive mind at work against you.
The last mind then is what we call the somatic mind, that mind which works well below any conscious awareness and which governs the organs of the body. It keeps the heart beating, the cells replicating, and so forth.
The final component of this trio is the spirit. This is actually you. It is what you are, the spirit. It is you who looks at pictures in your mind. It is you who decides to move the body. You are the life force that animates your body. You are the one who decides what the body will do. You look into the mind to solve your problems, and then with your solution give the command for the body to execute the decision. You are not the small life force within the cells of your body, but a separate and larger life unit that runs the entire organism.
So what is death? When the body dies you o not die. You separate from the body, move on. There are plenty of people who can describe the experience of during an operation, or accident, looking down on their body and the scene around them. For some they think they maybe almost died, as they have separated out from their body. But actually that is not always necessarily true. During periods of high pain a being will exteriorize from the body. He can often be found watching the proceedings and then re-enter when it is deemed safe. If he was a Scientologist he would then able to counsel out the experience and memory so as to not leave any negative after effect.
I hope this helps and there is much more in books on the subject by L. Ron Hubbard, the founder of Scientology.