What are artificial sugars?

It depends on who is talking and what they mean. There are many kinds of sugars in nature, and still more that do not occur in nature but that have been made in the laboratory and that is what makes them artificial. They are not important in day-to-day use, because they are expensive and usually useless as well.

One also could make sugars that one does find in nature, and because you had made them artificially, that would make them artificial even though they were the same as the natural sugars. Think of high fructose corn syrup for example. People break starch down into glucose (which is "making glucose", if you like) then they treat the glucose with a natural enzyme that twists part of the molecule so as to swap the positions of a few atoms, and that turns it into fructose, much as twisting a piece of wire can make a paper clip. The wire wasn't a paper clip before you started, but is now. Similarly the molecule wasn't fructose before, but is now. But fructose is the same sugar one finds a lot of in fruit, so it is natural even if it is artificial as well.

However, some people speak of "artificial sugars" or "artificial sweeteners", when what they mean is "sugar substitutes". Some of the sweeteners aren't really artificial, but come from plants, but none of them are sugars, artificial or not. Examples of such chemicals are saccharine, Aspartame, and cyclamate. Some that are not artificial are stevia, sorbitol and thaumatin.