There are two main automatic focusing modes to choose from: single shot or continuous
Single / One Shot
You can’t take a shot until the image is in focus. Once the camera has acquired focus, it stays locked at that distance, and you’ll need to take your finger off and back on the shutter release to refocus.
For everyday subjects, use Single Shot AF, as this won’t let you take a picture if the subject is blurred.
Left to the camera, the focus might be locked on the tip of the nose, so use a single AF point to focus on an eye.
Set an aperture of around f/11-16, and use Single Shot AF to lock the focus about a third of the way into the scene. Continuous/Servo
The camera will continuously focus the lens while the shutter release is half-pressed. The focus is never locked, and you can press the shutter to take a picture even if the subject isn’t in focus.
Continuous AF keeps action in focus. Some cameras allow you to customise the focus for different subjects.
Zooming a lens can cause a sharp image to blur, but continuous AF will adjust the focus as the lens zooms.
Shooting from a rocky boat or a vehicle on the move? Use continuous AF to adjust the focus while you’re in motion.