Carbohydrates are being (to a certain extent) metabolized in your body as glucose, one of the fuel sources in your body.
Looking on the nutritional table of packages, there are three main types of carbs:
Fibers are carbohydrates, but won't raise your blood sugar levels and will not trigger insulin. Basically, the fibers will buffer the effects of the carbohydrates turning into sugars (releasing them more slowly). You can calculate the net carbs as follows:
net carbs = gross (total) carbs - fibers
An example: You buy a package of rice. Per 100 grams, the total amount of carbs is 68 grams. 0.4 grams of this are sugars, and it includes 6 grams of fibers. The net carbs will be: 68 grams - 6 grams = 62 grams