You can see your layout in 3D from various locations by selecting "3D View" from the Window menu.
If there is a train on the layout then you can select one of several train views:
Normal View
View from cab
Walkthrough View
If "Walkthrough View" is selected then you can "walk" around your layout using the keyboard. Keys can be customized in the "Preferences" dialog that appears when you select "Preferences...". In the case of MacOSX there is "Preferences..." menu item under the "googol-Choo-Choo 3D" menu. In the case of MacOS 9.x there is it under the "Edit" menu.
Go Forward : up arrow or W Go Back : down arrow or S Left Turn : left arrow Right Turn : right arrow Left Step : A Right Step : D Jump : Space Move fast : Shift
Light Setting
There is only one light source in 3D view. You can set the location of the light source in the Control: Light window. The Y slider is up and down, the X slider is left and right, and the Z slider is forward and backward. If the "Set on train" checkbox is checked then the light is place on the front of the train with the camera.
Control: Light Window
Export Image & Movie
The 3D View can be exported as an image file (PICT,JPEG,BMP) or QuickTime movie. Select "Export..." from the File menu.