Screen Sharing gives you an opportunity to take the stage and present the board to other participants. Let your boardmates follow your actions by clicking Screen Sharing in the bottom left-side corner of the board:
Screen Sharing menu
Once you click Screen Sharing > Start your app screen gets outlined in blue, and other participants see a pop-up window indicating that the screen sharing session is on. Your boardmates can Join your stream, and see exactly what you are seeing, following your actions, listening to your comments and seeing your cursor highlighted.
The screen sharing window shows the list of watchers. There's also an option to enable or disable your microphone for voice-over comments.
List of watchers