The Arabs probably discovered the process. They distilled perfume components and other mixtures of fermented materials. Many of these were prepared for medicinals. By the 15th century, the English and Scots had begun distilling barley beer and, in the 16th century, cognac was prepared in France. Whiskeys were made in a similar way.
Whiskeys are aged in barrels.
The inside of these barrels is often charred. The barrel provides some of the flavoring materials. It is aged for at least two years in new, charred oak barrels. These beverages can be distilled from just about any fermented mixture including potatoes, grains, etc. Rum is made from fermented molasses or sugar cane juice.