Sugar is a carbohydrate similar to starch.
All natural foods contain different type of sugars. The natural sugar tends to be released more slowly and absorbed better into the bodies blood system.
The added sugar from food substances such as chocolate, soft drinks, fruit juice and jams are known as empty calories as these contain no other nutrients.
This is one reason sweets and chocolates are no good, because they have no cellular structure and just release high sugars within our blood streams.