No added sugar or unsweetened
'No added sugar' usually means that the food has not had sugar added to it as an ingredient. And it is food containing added sugars that we should be cutting down on.
Sugars also occur naturaly in food such as fruit and milk, but we don't need to cut down on these types of sugar.
So this means that a food that has 'no added sugar' might still taste sweet and might not have a low sugar content.
The food might contain ingredients (such as fruit) that have a naturally high sugar content, have added milk, which contains lactose, a type sugar that occurs naturally in milk, or an artificial sweetener may have been used to give the food a sweet taste.
'Unsweetened' usually means that no sugar or sweetener has been added to the food to make it taste sweet. This doesn't necessarily mean that the food will not contain naturally occuring sugars found in fruit or milk.
The ingredients lists on 'no added sugar' and 'unsweetened' labels will tell you what ingredients have been used, including what types of sweetener and sugar, and you can find information about how much sugar there is in the food in the nutrition panel.