Focus and exposure are maintained where the blue AF point is displayed while you press the shutter button halfway. This helps you avoid missing shots of subjects in motion.
For assistance with Bluetooth pairing between the camera and a smartphone, please see this article: https://support.usa.canon.com/infocenter/index?page=content&id=ART173357
Enable Helps avoid missing sudden photo opportunities, because the camera constantly focuses on subjects until you press the shutter button halfway. Disable Conserves battery power, because the camera does not focus constantly. However, this may delay focusing.
Use a commercially available blower to remove dust from the lens. For hard-to-remove dirt, contact a Canon Customer Support Help Desk. ID: 8201031700_EN_49