Why Do I Hear an Echo?

If everyone is using headphones, and has their audio devices set correctly, you shouldn't hear an echo.

Someone around you may have their input settings wrong or may not be wearing headphones at all. If you don't have headphones, check the "Enable Echo Cancellation" box in your audio settings, seen below: 

Audio menu with Enable Echo Cancellation checked

After turning this on, you may hear an echo for another few seconds as the software adjusts.