When you open a new document in Wirecast, only the Live area is shown. The Live area shows what is sent to your viewers (though what you see in the live area is before the encoder/compression).
When AutoLive is off, you can make several changes without your viewers seeing the change. This is most useful when you are using an engineer to run your broadcast.
When you do several changes without your viewers seeing them, you most likely want to see what those changes will look like to your viewers. This is what the Preview is for.
To see the preview, you can select "Preview" from the "Layout" menu in Wirecast.
Here, the main window shows both the preview (on left with green "P") and live (on right) displays:
In the above example, AutoLive is off, "River" is the current Live shot (what the viewers would see if you were broadcasting), and "Ripples" has been selected and is in Preview.
If you press Go button button, the "Ripples" shot becomes Live, using the "Smooth" transition.