What type of sugar is considered good sugar and bad sugar? and what harm will it do to eat one piece of candy every now and then?

Complex sugar better: A candy now and then is fine.complex sugars like in fruit--cherries,strawberries are much better than table sugar or sugar in drinks

Eat Quality Carbs: Enjoying candy in limited quantity is allowed. Processed foods are often sweetened with table sugar (sucrose), fructose (fruit juices), corn syrup & offers minimal nutrition or fiber but lots of calories. Complex sugars found in fruits, vegetables offer nutrients, fiber & more. Do limit Carb intake to 45-65% daily calories. See more info at: http://www.cdc.gov/nutrition/everyone/basics/carbs.html