Eons of emergent changes and mutations, aided by natural selection, have made it possible for cells to make efficient use of the available energy on this planet. And the source of this energy is the Sun.
With these two sentences we welcome what can be considered the hardest, and most despised, part of any Bio course: Cellular Respiration. Cells are powered by combustion; but these have to occur in a controlled way. Enzymes–a synchronized and highly complex cascade of enzymatic events– will manage this controlled release of energy. This process begins with Glycolysis. The following videos are very good explanations of how Glycolysis works. Keep in mind that these are complex events. They are summarized as best as possible, but some effort has to be put in order to understand them: