Welcome aboard. In brief, the fly types you're asking about are:
Dry flies - These imitate the adult stages of insects when they are on the surface of the water, either after emerging from their nymphal shucks or landing on the water to lay eggs.
Wet flies - These imitate emerging insects and many other forms of tiny underwater life that fish might find edible. These flies are most often fish on the swing (with a tight line) so that the current can impart action against the flyline and move the fly.
Nymphs - These are usually weighted and imitate the nymphal stage of insect life, which almost always occurs on the bottom of a stream, river, lake, or pond. When fished in moving water, these flies are usually fished with a dead drift, meaning that they are allowed to tumble naturally with the current like a real nymph would.
As far as internet resources go, you don't need to search any further than where you already are. This site's members can answer most questions, and we often get together to fish in small or large groups. New faces are always welcome.