The three lessons that clarify the substances this lesson refers to are: Carbohydrates - Simple Sugars, Complex Carbohydrates - Starches, and Complex Carbohydrates - Fiber.
Simple sugars and starches begin to break down in the mouth and continue through the digestive system untill fully broken down. The end point of digestion for them is the small intestine. Maltase, sucrase, and lactase are enzymes specifically on the villi. The villi are like really small shag carpeting on a thin hump--now multiply them by the nth degree and you have most of the lining of the tube that is your small intestine. (Of course, make the shag carpeted hump microscopic.)
Maltase breaks down maltose. It becomes 2 glucose molecules and is absorbed into and carried by the blood stream up to the liver. Sucrase breaks down sucrose into glucose as well, but sucrose also has a component that breaks down into fructose. This, too, gets carried to the liver. The lactase gets broken down into the molecules glucose and galactose and is liver-bound.
You see that glucose is a component of all three of these. The glucose is both stored and taken by the bloodstream to the cells that need it. Fructose and galactose are also used for energy, but can also be converted into glucose.
As was discussed some in the Fiber tutorial, both insoluble and soluble fiber have components that are impossible for the human body to digest. This still serves a tremendously important purpose. The mechanical function of the intestines needs bulk to help push waste through, and undigested fiber provides this. It is a pace that is just right, too. Waste keeps moving, but not so fast that the beneficial bacteria aren't able to do their thing. Plus, glucose levels are kept more stable and cholesterol can be absorbed.