The L28 is suppose to automatically focus when you lightly press and hold the shutter button Halfway down. You should hear a sound and the focus brackets in the center of the screen should lit green. The camera will take the picture without focusing properly if you press the button too hard.
In Scene Mode/Easy Scene Mode, the camera uses face detections when Portraits, Night Portrait, and Pet portrait scenes are selected. A yellow box will show up around the face of a human or pet such as a cat or dog, and when the shutter button is lightly pressed halfway down, the camera focuses on the face. See page 57 of the user manual.
When the camera is set to Auto Mode (Not Easy Auto). face detection cannot be use. The camera uses the center of the screen to focus and the focus brackets in the center of the screen cannot be moved.