For MENU options, click on picture with right mouse-button.
These provide:

Rotation Start and Stop
Selection of atoms, residues, chains, etc. for further action
Display options, including various rendering options
Other options, including Slab Mode, Specular rendering, Stereo (crossed-eye stereo pair)
Coloring options
File options

To rotate about x or y axis, use left mouse-button, move pointer on image.
To rotate about z axis, use Shift and right mouse-button, move pointer horizontally.
To zoom, use Shift and left mouse-button; move down to zoom in, up to zoom out.
To pan, use Ctrl and right mouse-button.
To slice when in Slab Mode, use Ctrl and left mouse-button.

3-D Viewing
Try the following, using a simple, well defined image:
Sit so that your eyes are about 2½ to 3 ft back from the screen. Make a frame by putting up both hands palms out vertically about 1 ft in front of you, with thumbs extended, pointing towards each other and overlapping, and forefingers about 2½ inches apart. Move this frame to and fro between your eyes and the screen, until you can see only the left picture with your right eye, and only the right picture with your left eye. Now open both eyes, and let your eyes relax. With practice, a single image in 3-D will form in the frame. The focus of the 3-D image appears to be in front of the screen. Further practice will allow you to dispense with the frame, when the 3-D image will appear as a third image between the two real images.

Further Hints

A nice page with more extensive hints for 3-D viewing of stereo images can be found here