REMEMBER that you can also record video answers with a mobile device (smartphone & tablet). No apps are required.
First, check that your speakers are turned on, and that your speaker volume is fairly high. Sometimes the microphone is just fine, but the speakers are turned off or muted. If you’re applying for a job, you can test the speakers easily by listening to video questions. If you’re an employer recording video questions, you can test the speakers by listening to music on your computer.
Chrome & Firefox
Check that you have allowed both camera and microphone from the address bar:
Check that the selected output is the correct one and the volume is not muted. You can access the sound settings from System Preferences -> Sound.
Check also that the input is the right one and that you see the sound bar moving while speaking: