Open an online speaker test that plays stereo tones — verify you hear audio in both left and right channels. Alternatively, go to System Settings > Sound > Output, select your speakers or headphones, and click the Balance slider to test each side individually. If there's no sound, make sure the correct output device is selected (check for HDMI, Bluetooth, or headphone overrides), the volume isn't muted, and the volume slider is turned up. Play a sound from a YouTube video or Music app to confirm system audio works. If sound works in the system but not in a specific app, check that app's audio output settings. For Bluetooth speakers, disconnect and reconnect if audio cuts in and out. If nothing works, restart the audio service: open Terminal and run "sudo killall coreaudiod" then test again.