Hello and Welcome Izzy,
please also see...
http://en.wikipedia.org/wiki/Carbohydrates
Carbohydrates are chains built from the simplest monosaccharides: like glucose, fructose and galactose.
These chains increase in complexity: from disaccharides such as sucrose (table sugar) which is built from glucose + fructose, or lactose (in milk) which is galactose + glucose... all the way up to the polysaccharide cellulose/fibre which humans are not supposed to be able to digest --
ruminants such as cows have enteric flora which can digest cellulose to extract the sugars.
These chains (with the possible exception of cellulose) are broken down by our digestive system using enzymes and other methods.
The "of which sugars" shown on the nutrition labels is comprised only of the simpler monosaccharides and disaccharides. The difference between the "Carbohydrates" amount and the "of which sugars" is technically termed "Starch" and this is comprised of polysaccharides other than fibre. In all cases these "Starches" will tend to raise your Blood Glucose sooner or later and in many cases of processed/packaged foods it will likely be just as soon as if you had eaten plain glucose.
In other parts of the world the label shows "Total Carbohydrates" with sub-totals for "Sugars" and "Fibre" but also does not show the "Starch" sub-total.
So many words that can all mean higher BGs
and words like "Sugar" that can have subtly different meanings.
This layer of confusion built into the nutrition label, is I suspect, ripe for exploitation by the food manufacturers... for example by removing the sucrose (a "Sugar") from a product and replacing it with a "Starch" like maltodextrin (which rapidly digests to glucose) they can claim "No Added Sugar" on the label -- but the product is just as sweet and has just as much impact on BG as before.
So it becomes important to also read the list of ingredients to weed out these hidden sugars.
There is yet another potential trick: the ingredients are listed by quantity (more quantity = higher up the list) so by breaking the "sugar" into different types, they can list each of them scattered and lower in the list, whereas in a straightforward recipe it would be much clearer how much sugar it contained :?
Here's an example of an ingredient list for McD's special burger sauce -- spotted in a post earlier today -- I count at least 3 sources of carbohydrates that are likely to rapidly impact BGs..
Water, Vegetable Oil (Soya Bean Oil), Diced Gherkin, Sugar, Spirit Vinegar, Modified Maize Starch, Free Range Egg Yolk, Mustard Seed, Salt, Preservatives (Acetic Acid, Potassium Sorbate), Mustard Flour, Stabiliser (Xanthan Gum), High Fructose Corn Syrup, Natural Flavourings (contains Soya), Dried Garlic, Spice, Colour (Paprika Extract)
Good luck! Please stay around, read, share and ask questions