You must click on the appropriate box in the “Participants” section next to the name of the participant to which you want to give a right. A “X” in the box means that that participant has the right to use the device in question. There are three types of rights: camera, microphone and annotations tools.
If you want to give a right to all participants at once, simply click on the icon of the device to which you want to give all participants the activation right directly above the checkboxes in the list of participants.