The first layer of reality, so called because it can be experienced as opposed to merely thought about, is the material elements composing all objects of the physical universe. The earth element is the element of extension, experienced as the hardness or softness of objects. The fire element is the quality of heat or cold. The air element is vibration or movement. The water element represents fluidity and cohesion, the element responsible for holding things together, such as adding water to dry flour. Along with these elements arise secondary characteristics of matter — color, odor, taste.
The whole physical universe can be experienced in terms of these elements. One can become aware of them, free of thought about them. Floor is a concept; floor does not exist. What is experienced is the feeling of hardness or coldness, or color. The eye sees color. It does not see a name. When walking out of doors, most people see "tree," but that's a conceptualization of what is seen. What is actually seen is color in a certain form. Another process of mind then labels that "tree." "Body" is a concept. What is experienced is sensation: heat or cold or pain or tension, the workings of the elements only, all of which are in constant transformation. One can be aware on the experiential, non-conceptual level of things as they are, aware of the qualities of the sensations without being attached to the concept, without projecting some idea onto the experience.
It is interesting that concepts remain static while reality is always in flux. The concept "body" stays the same but the body itself is always changing.
The second of the ultimate realities is consciousness. Consciousness is the knowing faculty. Sometimes people have the idea that in this mind-body, there is one consciousness from birth to death, one observer who is knowing everything. This idea gives rise to the idea of a permanent self.
Consciousness itself is arising and passing away in each instant. There is not one mind which is observing all phenomena; at every instant "mind" is created and destroyed. The consciousness that hears is different from the consciousness that sees, or tastes, or smells, or touches, or thinks. There are different mind-moments, arising and passing away every instant. When the mind becomes very alert, it is possible to observe this flow of consciousness, and understand that there is not one knower, one observer, but rather an ongoing process at every moment. This exposes the illusion of a permanent self.
Source: Paraphrased from "Concepts and Reality" in The Experience of Insight by Joseph Goldstein