In the virtual training room participants can talk to each other via VOIP (voice over IP).
For the host- the microphone is activated by default. He can mute himself by clicking on the "talk" button in the toolbar.
For guests- Speech is disabled by default. In order for a guest to be able to talk, the host must first allow participants microphone by clicking the "allow guest mic" in the participants panel. That will enable the guests "talk" button which can subsequently be used the same way a host does.