If you have not used Protein Explorer (PE) before, there are introductory flash movies Getting Started in Protein Explorer, and a one-hour tour available from PE's FrontDoor.
To begin self-directed exploration, scroll the control panel if needed until you can see a cluster of convenience buttons (Spin, Zoom, etc.). Beneath the cluster of buttons are links to QuickViews and the PE Site Map. Use these to access PE's other control panels, for self-directed exploration.
When you wish to return to the presentation, find the cluster of buttons in the current control panel, and open the PE Site Map. At the top of it will be the title of the presentation, as a link back to the presentation.
To identify atoms by clicking on them with the mouse, you need to make Protein Explorer's message window visible. To do this:
Macintosh:
Here are step-by-step instructions.