To make it, whether in home stills or factories, cornmeal is put in vats with water and enzymes that convert some of the corn to sugar. Yeast added to the "mash" converts the sugar to alcohol. In a few days, the alcohol concentration tops 10 percent and the yeast goes inactive, having, ironically, rendered its own environment toxic.
Distillation increases the alcohol concentration: 50 percent is vodka, 95 percent is fuel. Alcohol vaporizes at a lower temperature than water, so heating the fermented mash turns the alcohol to vapor that collects on a cold condenser.
Uh, okay. The process is illegal, dangerous, unlikely to help the environment all that much, and possibly hazardous to all of our long-term respiratory health. Other than that, it's great! Find your lab goggles and get to work!