The pepper-box revolver or simply pepperbox (also "pepper-pot", from its resemblance to the household pepper shakers) is a multiple-barrel firearm, mostly in the form of a handgun, that has three or more gun barrels in a coaxially revolving mechanism. Each barrel holds a single shot, and the shooter can manually rotate the whole barrel assembly to sequentially index each barrel into alignment with the lock/hammer, similar to operating a revolver cylinder.
You can use a weapon that has the Ammunition property to make a Weapon Ranged Attack Roll only if you have Ammunition to fire from the weapon. Each time you Attack with the weapon, you expend one piece of Ammunition. Drawing the Ammunition from a Quiver, case, or other container is part of the Attack (you need a free hand to load a one-handed weapon).