I cannot be heard / I do not hear anybody
First, make sure that you set up your audio device correctly within your operating system!
When you enter a conference you will be asked how you want to connect to the audio session. It is always recommended to choose "with microphone". Do not forget to allow the browser/session to take control over the audio device. If that does not help, please leave the audio session (telephone symbol beneath the presentation) and join anew. Also leaving the BBB session entirely and signing back in can fix the issue.