Understanding the mind is paramount to understanding Buddhism
In many Buddhist writings, you will read about the “Five Skandhas”. This is very simple, and is again, Sanskrit for the constituents of the mind.
They are split into two, those being “form” Skandhas, and “mind” Skandhas.
The Five Skandhas, also called Formations are:
form
apperception, sensibility or feelings
perception
volition (will, impulse)
consciousness
1. Form is composed of matter made up of four elements: earth, water, fire, wind. Form is conceptual, and should not be grasped at, or held important.
2. Apperception or sensibility is derived from the sense organs:
1. eye enables sight
2. ear enables sound
3. nose enables odour
4. tongue enables taste
5. body enables touch
6. mind enables the experiences of the five organs above, but also of its own function called “knowing”
This set of pairs, i.e. organ + function, is known as the Twelve (12) Bases of Consciousness.
3. Perception is a product of the six externals above: sight, sound, etc. It is the individual's processing of the 12 bases to 'feel' the environment
4. Volition is the reaction of the will to the objects and may produce aversion, attraction, etc. In other words, the feeling as basis for emotion.
5. Consciousness grasps the qualities of the six objects. It creates a third member of the sets in 2 above. These are designated Visual consciousness, auditory consciousness, and so on, ending with mental consciousness. These are called the Eighteen Elements [dhatu].
These five aggregates or formations, the skandas, are not ultimate and eternal in nature but are conditioned. They arise from causes and circumstances. Like all phenomena, they come and go; endure and change and disappear.
Since we are composed of these, we are impermanent. There is no part of us that is eternal. We cannot logically say, "That is mine; I am that; that is my Self" This is what Buddhist call “the endless wheel of life and death”
The quite amazing upshot is that “existence, as we see it, is illusionary and conceptual”
Called the "Five Aggregates" because in turn they too are not solid indivisible whole entities and are made up of even smaller parts. The break-down [can go] on and on, until there is not even a single particle which one can call a Self. They only come together as an "aggregate" due to causes and conditions. Since it does not have an unchanging self and is impermanent (i.e., when the causes and conditions are gone, so is it ;) it is EMPTY.
This is the subject of the Heart Sutra!