Move the NCV sensor so that it's close to the wire or circuit. If there's live AC, the multimeter will begin beeping and the top indicator LEDs will light up.

If the NCV detects ~45-100V, a single green indicator LED will light up, and the screen will display "L".

If the NCV detects above 100V, two red indicator LEDs will light up, and the screen will display "H".

Most of the time, you can detect which wire in a power cable is live by touching the NCV sensor along each edge of the cable.