A common problem with Webex sessions is that the audio seems to get stuck, so some participants cannot talk to others.
For some reason, the Webex app often has video enabled, but not audio. If you go directly for the green Start My Video button, you will not hear anybody, and nobody will hear you:
Instead, click on No Audio and select Call Using Computer. The green button now changes to Connect Audio and Video:
Click on it to start your session. If required, you can also adjust the microphone and loudspeaker settings.
If you have missed to select the audio connection, you will see a button with a classic telephone handset. Click on the button and select Call Using Computer from the appearing menu:
If required, you can also adjust the microphone and loudspeaker settings.
Ready to go
In either case, the left button now changes to a microphone symbol with a green dot, and everything should work fine: