Before manufactured sugar became available, people used honey. Today sugar is a major product and is derived from several plants. Sugar occurs in small amounts in most plants. In the plant, sugars are converted to starch for storage as an energy reserve. This process is reversible.
Enzymes catalyze the reaction.
Sugars are water soluble, whereas starch is not. The process also can be catalyzed chemically. In general, cost determines what can be used as a sugar source. A major use of sugar is as a preservative for food products. This is sold and used as high fructose corn syrup.