In simple terms, sugar is used by the body for immediate energy. Unused sugar leads to an increase in fat stores. All carbohydrates ultimately break down into sugars (which is why so many people fear carbs), but different types of carbs break down differently. Whole wheat has become so popular lately because it breaks down slower in the body than white flour, allowing for a more steady release of sugar into the blood stream to be used, without having the body be overloaded with sugar all at once, and storing the unused sugars as fat.
Carbs/sugars are necessary for humans to function optimally, but consuming them in excess inevitably leads to weight gain.
sugar
It's not as much about the sugar itself - it's about how much of it you eat. Sugar contains a lot of energy that your body can use, but if you don't use it up your body will turn it into fat and store it instead.
This is a good sugar substitute and you can use this to replace sugar. This can also heal scars on the body if used externally.
sugar and starch
The easiest thing for the body to use for energy is glucose, basic sugar. It can make ATP from this which is what powers the body.
insulin
Carbohydrates are acted on by enzymes in the body to convert them to sugar so the body can use them as fuel.
glucose
One concern is that most sugar free drinks use a sugar substitute, which can sometimes be worse for your body.
Sugra is the easiest source of energy for your body. W/o sugar the body has to use fat or proteins, break these up into sugar for fuel. That's a slower process which means you can't work as hard.
If you are you asking about how much sugar does your body have, then that is calculated by how much you have consumed recently. All food that is packaged has a label on it listing its carbohydrate content. You can use that to help you start keeping track of it.
They are sugars that the body can use directly, unlike complex sugars which the body has to first break down. Glucose is an example.