Well, cholesterol is a steroid of fat and the primary sterol synthesised by animals, which are by far its primary natural source. Some types of cholesterol are good and necessary while others are harmful, and having high levels of them in your blood can lead to heart disease and clog your arteries.
Carbohydrates are saccharides, or sugars. They give animals energy. They are also necessary in moderate quantities, but consuming large quantities of refined simple carbohydrates is what makes people overweight.