The attendance list will show you all of the attendees currently in your session and their role. Typically you, as the lecturer, will be the Moderator and students will be the Participant. To the right of each attendee is a gauge giving you information about their connection to the network and to the right of that is a button that will give you further actions you can take on the individual attendee.
From here you can send a private message to the individual, change their role in the session or remove them completely from the session. Moderators have full control over the session and you would typically only have one or two per session. Anyone who needs to share content with the session will need to be ‘upgraded’ to Presenter.