Three most used types of spirits you should know to succeed in the bar industry.
Whiskey is a spirit distilled from grain mash. These grains—which can also be malted—can vary from barley to corn to rye to wheat. Perhaps the most strictly regulated spirit across the world, a spirit qualifies as a whiskey based on fermentation of grains, distillation process, and aging in wooden barrels. Despite that, however, there are several different classes and types of whiskey, generally categorized by its region of distillation.
Rum is a spirit distilled from sugarcane [byproducts]. It can also be distilled directly from sugar cane juice (as in the Brazilian form, Cachaca). Like vodka, it is usually a clear liquid, but rum is sometimes aged in oak barrels, which gives it a dark color. This is also how you rum is graded. Light rum, for example, is “purified” to remove impurities and color and generally not aged. Gold rums can be aged slightly (or simply not purified in the same way as light rums). Dark rums can be aged in casks (to get the color, and the characteristics of the barrel) but also can be distilled from molasses, which is naturally darker. There are also flavored and premium rums that involve different distillation and production processes.
Vodka is, essentially, the purist spirit you can drink. It basically ethanol cleanly distilled from a neutral grain or potato, and water. The spirit is traditionally drunk “neat,” which means not mixed with any water or any other mixer and not served with ice, though it is more commonly served chilled than at room temperature. Because it such a “clean” spirit—with little impurities and, thus, little “flavor”–it is an ideal spirit for mixing into cocktails.
Of course, there are other types of alcohol served in bars around the world, but these are, perhaps, the three most common.