They also offer some focus area modes that use just the one focus point you have selected or some other focus area mode that help keep things in focus in your photos.
Auto Focus Modes
Single Servo Focus
The most commonly used focus mode is Single focus. (Nikon - AF-S, Canon - One Shot AF)
Use single focus when you are making photographs of subjects that aren't moving.
When the shutter is pressed halfway the camera focuses, turns on an in-focus indicator in the viewfinder, and then locks the focus until the shutter is released, or until the shutter button is returned to it's normal position.