To make alcohol at home, we need to ferment some sugars. The sugars in corn or potatoes or wheat work for this. Mash up some corn, mix with water and heat it to a certain temperature for a certain length of time to release the sugars. Add in some proper yeast at the proper temperature and length of time and let the yeast do its thing. When the fermentation completes, you'll get about 13% EtOH. Now, we need to concentrate it down by separating the EtOH from the H2O. That step is distillation. It's done by heating the liquid and taking advantage that EtOH will boil off at lower temperature than water. Now we have water liquid and EtOH gas. Cool down the gas and it's back to a liquid. Fermentation is mostly legal. Distillation is mostly illegal. Since it's illegal to do at home, it's moonshine. Done legally it neutral grain spirits. Of course there are flavors left over from the corn as some impurities