Why can't I hear people speaking? Why can't people hear me?

Check the following:

• If you’re using an external microphone, make sure it’s plugged in to your computer. Also, check that your microphone is selected in your browser microphone settings.
• In your computer’s web browser settings, check that your browser allows websites to use the microphone. For example, in the Chrome web browser:
  

• Make sure you haven’t muted yourself or others.