Press down on the knob next to your fireplace pilot light and turn the dial to the "Pilot" setting. Release the knob.
Press the knob down again, then use the thumb on your other hand to repeatedly click the igniter button. Clicking the igniter button will light the pilot light, but it could take up to 45 seconds of clicking. It's important you hold down the knob while you click the igniter button because that opens up the gas line so gas reaches the pilot light.
Release the knob once you light the pilot to close the gas line. If the pilot light quickly burns out, wait two minutes and try again.
Rotate the knob from the "Pilot" setting to the "On" setting once you light the pilot light and it remains lit. There's no need to light gas fireplaces pilot lights every time you use the fireplace, because the pilot light will stay lit.