Start the avionics via starting the aircraft or by flipping the mains on (battery and power system buttons) and then flipping up the avionics switch. Let the IC-A210 go through its start-up procedures.
Tune the left-hand display to your desired frequency, most often either ground or ATC (tower). Set the right-hand frequency to your secondary frequency, such as ASOS or ATIS (weather and air notice channels).
Plug in your headphones and listen for broadcasts on the secondary station (most common for start-ups, as you need to check current conditions and weather). If squelch is present, press the volume dial in and release.
Check the digital readout on the right and make sure it reads "Test." Turn the volume button up and down to remove the white noise or static. Once the static is gone, press and release the volume dial to return to your frequency and use the volume dial as normal.