All shotguns have some of the same basic components. Starting from the end nearest to the shooter, there's often a stock that allows you to steady it against your shoulder muscles. Some manufacturers put a recoil pad at the end of the stock to help dampen the kick you feel when you fire it. There are some shotguns, usually "assault" style, that have foldaway stocks or no stock at all. Moving forward from the stock, you'll find all of the parts associated with firing. This includes the trigger that connects to the sear and hammer. Some shotguns have a pistol grip that extends downward below the trigger.
The hammer activates the bolt assembly and firing pin, which rests against the cartridge to be fired. Now we're at the chamber, where the loading, unloading and firing happens. The chamber can be accessible from the side or the top. Connecting to the chamber is the barrel, which is the long tube that the ammo travels through as it leaves the gun. Some shotguns have a magazine connected to the chamber -- this may take the form of a second, shorter tube below the barrel or else a drum or rectangular cartridge that snaps into the barrel. There may also be a fore-end (a sliding handle colloquially known as a pump) attached to the shorter tube, which is used to partially automate the loading and unloading process. On the top of the barrel, you'll often find a bump that's used as a crude sight.