The first and second laws of thermodynamics relate to energy and matter. The first law states that matter and energy cannot be created, nor can they be destroyed. The second law states that entropy never decreases; entropy can only increase.
While, according to the first law, matter and energy must remain constant in quantity, the quality of the matter or energy deteriorates gradually over time to become more disorderly and chaotic. Entropy refers to the quantity of unusable energy in a system. As a system increases in entropy, the quantity of usable energy is converted to an increasing quantity of unusable energy.