Your computer needs a microphone. Make sure you give permission to enable your microphone, if asked. If you are in the Virtual Museum, you can access your microphone and voice chat settings via the Quick Access Menu (Icon with 6 dots) in the right corner of the navigation bar. You can toggle the buttons to enable/disable your microphone and voice chat.

If you are in the Virtual Museum, you can change these settings in the Quick Access Menu. Click on Participants to see the list of all the other museums guests. Click on the button with the speaker Icon next to the visitor you want to mute/unmute.