Pistols (Semi-autos) use part of the energy produced by burning cartridge powder to remove the used cartridge from the chamber, cock the hammer (or striker) and load a new cartridge in the chamber, so the pistol will be ready for the next shot. Cartridges are usually fed from a box magazine, located in the pistol's handle. Box magazines may contain up to 15 cartridges (or more) in single or double columns, depending on the pistol model, and are easy (and very quick) to reload.
Revolvers got their name from the rotating (or revolving) cylinder, which contains cartridges. Usually the cylinder holds from 5 to 8 cartridges.