I think the answer is into the question. Wet flies work under the water, and dry flies remain floating on the surface of the water. Wet flies can be nymphs, emergers, streamers, hatching flies, or other types of larger bait. On the contrary, dry flies can resemble full-grown flies, insects, etc.
Another significant difference between wet and dry flies is the size of the flies. Wet flies usually run from a size 10 and larger. Dry flies typically run from a 12 and smaller.