As another way of saying it, every pistol I know of needs to have a cartridge put into the chamber. On 99% of guns, this would be accomplished by placing a loaded magazine into the pistol, racking the slide backwards and letting it fall forward.
One thing that may lead to confusion is sometimes in movies, the slide will already be locked in the open position, the shooter will insert a loaded magazine and drop the slide... When this is shown, it might make it looks like less is going on than really needs to go on.
On some smaller Berettas and Taurus pistols, the barrel can pop up allowing the round to be chambered without racking the slide - you insert a loaded magazine, pop the barrel up, place a round directly in the chamber and push the magazine down... and there's not need to rack the slide.