Screen sharing tools allow your students to see what's happening on your computer screen in real time.  Not only can they see the windows open on your computer, but they can also see the mouse movements, keyboard strokes, and anything else happening on your screen.  Some tools, like Join.Me, also provide conference call and chat features for free, and allow you to give collaborators control of the shared screen.  The video conferencing tools Google Hangouts and Skype now also offer limited screen sharing.  

Join.Me is a free screensharing, conference call and chat tool.  To share your screen with others, just give them the unique code provided for that session.  You can interact with participants vocally through the conference call feature or with the chat message feature.  Demonstrate and communicate with remote learners in real time by screen sharing!