much simplified
cocked - functionally and mechanically prepared for firing,
on most weapons the next step is aim and pull the trigger.
Revolvers after firing one shot must be manually moved to the next shell chamber and again cocked. In single action revolvers this is accomplished by pulling the hammer back. In double acting revolvers this action may be accomplished by pulling the trigger thus also firing the round. You can cock the double acting revolver by pulling the hammer back.
In semi automatics, the rounds/shells/bullets are stacked in a rectangular spring loaded clip mechanism that feeds into the firing chamber. These weapons may be cocked either by pulling the hammer back (if there is already a round in the chamber) or by retracting the slide mechanism on the top(this action feeds another round into the chamber, cocks the weapon. This sequence occurs automically after firing a round (hopefully ~ LOL)and ejects the spent shell casing simultaneously. Thus the name "semi automatic".
True automatic weapons continue firing so long as the trigger is pressed and fresh cartridges are fed into the firing chamber. Semi-automatics require a specific trigger pull per shot.
In old movies, we would see the gunslingers pulling the hammer back with the heel of his free hand. This was called fanning and provided a rapid firing capability.
In more modern war movies, usually only officers carried pistols and generally they were semi-automatics. We would see them grab the top of their weapon, pull the slide rearward, and release, ready to fire.
There you are. More than you wanted. Subject to correction by experts.
