Clean dirty shells with an old toothbrush and water. A little bit of baby oil can make many shells shiny. Go to a museum or nature center that has a shell collection. See the wide variety of shells and how they display them. Visit a shell club or shell show to get ideas.
Libraries can be a great place to learn about shells.
Read a shell book. Pick one shell that you found and try to find the same kind in the book. During the day, most live land snails are under rocks and pieces of wood. At night they come out to eat, especially if it is damp from a recent rain. Along a seashore, big rocks away from the surf are usually good places to look for live snails.