Answer:
NAD - nicotinamide adenine dinucleotide
FAD - flavin adenine dinucleotide
Basically, NAD and FAD carry electrons to the electron transport chain in the inner mitochondrial membrane. These electrons are deposited near the beginning of the electron chain, and then these electrons are passed on from one protein to the next.
As these electrons move through the electron chain, they release energy, and some of this energy is captured in the form of an electrochemical gradient and used to make ATP.
Energy contained in the bonds of glucose is released in small bursts, and some of it can be captured in the form of ATP, a small molecule that is used to power reactions in the cell.
ATP = adenosine triphosphate