It will be helpful to decide if you have found a univalve or a bivalve. Univalves are the shells of gastropods. They are one piece and usually have a spiral. They are assymetrical. Examples are conches and whelks.
Bivalves have two distinct shells joined by a ligament.
Clams and oysters are examples of bivalves. Some are symmetrical. Keep shells away from direct sunlight and extreme heat. Pill vials and small plastic boxes are a excellent containers to store seashells. It is a good idea to put a small number on each shell and keep a log notebook of the data pertaining to that shell using the number to identify it.