First there is the body itself. The body is the organized physical composition or substance of Man, whether living or dead. It is not the being himself.
Next, there is the mind, which consists essentially of pictures.
Finally, and most importantly, there is the thetan. The thetan is not a thing. It is the creator of things.
Of the three parts of Man, the thetan is, obviously, most important. Without the thetan, there would be no mind or animation in the body. While without a body or a mind, there is still animation and life in the thetan.