|A shotgun is a common gun. It's different from a rifle and a pistol, mostly based on the ammunition it uses.|
It doesn't use bullets, it uses shells. A shell is a plastic tube with a primer, brass, gun powder, and shot (buck, bird, slug)
The shells store the bullets which can be very small bbs to a large lead projectile called a slug and other things in between.
They're usually simple to use and are useful for hunting up close (100 yards), home defense, and stopping power.
My first gun was a shotgun. They're usually easier to get than handguns but on the downside have a lot of recoil, that can hurt when you shoot them and be hard to control.
See the section on shotguns for more information.