The first button with letter A on it is continuous autofocus. This mode is fully automatic and works based on the camera libraries that the manufacturer has integrated into the device. The focus techniques also depend on the device. When the scene changes in this mode, the focus resumes searching until it decides it is in focus. 
To the left of the buttons is a focus position indicator. The focus on distant objects is the top of the indicator and the focus on near objects is the bottom.