WHAT DOES THE WHOLE UNIVERSE CONSISTS OF IN ITS MOST FUNDAMENTAL ASPECT?

That is an EXTREMELY broad question. It depends on the context of the question. The *visible* universe is made primarily of hydrogen with an assortment of other elements and massive particles that make up what we call "matter." Plus there's all those massless photons of light zipping about. Unfortunately, "matter" seems to make up only about 10% of the universe. The remaining 90% is called "dark matter." The substance that gives rise to the effects we attribute to dark matter has not been fully explored or understood, so the best answer to "what does the universe consist of?" is: we don't really know yet.

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