When using autofocus, what action should be taken to allow the camera to focus on the subject?

Pressing the shutter button halfway down is the correct method for allowing the camera to focus on the subject when using autofocus. This action activates the autofocus mechanism, prompting the camera to analyze the scene and lock in on the desired subject. Once you press the button halfway, the camera sends signals to the autofocus system to engage and determine the proper focus distance based on the detected subject.

Other actions like turning the focus ring or adjusting aperture settings do not directly facilitate the autofocus system in most modern cameras. Changing the shooting mode could affect how autofocus is utilized, but it doesn't directly engage focus on a subject in the way pressing the shutter button does. Thus, pressing the shutter button halfway is the standard and most effective method for achieving precise focus on your subject when using autofocus.