"Single action" means that the act of pulling the trigger only performs one function: releasing the hammer or striker, which strikes the firing pin or lever against the shell casing.

You'd have to cock the hammer of a revolver, or pull and cock the slide of a semiauto pistol for the trigger to function as single action.

Guns which cock and fire with one pull of the trigger are called double action.

When you eat dirt for the first time and leave your family to build a shack in the woods