Just as with revolvers, there are different types of semi-automatic pistols. The single-action version requires the shooter to cock the hammer by hand before squeezing the trigger to fire the first shot. After that, the gun fires, ejects the empty case, cocks the hammer, and loads another cartridge whenever the trigger is squeezed.
The double-action semi-automatic pistol allows the shooter to squeeze the trigger to fire the first shot. The double-action pistol does not need to be cocked manually before firing the first shot. Whenever the trigger is squeezed, the gun fires, ejects the empty case, cocks the gun, and loads another cartridge.
Semi-automatic handguns may have one or more safeties. Different guns have different types of safeties.