Operation Open the battery compartment,Insert the earplug to the hearing aid, then put the earplug in your ear, and move it up and down to insure it on the right position. Turn on the hearing aid, and then you can adjust the volume to get clear sound. Battery compartment on/off switch: Close the battery compartment completely, it begins to work, open the battery compartment, it will stop working. On/Off switch: Turn on or turn off the hearing aid. If you feel the whistling sound, please make sure if you have put the earplug, or if you have use a appropriate size earplug.