Install it using the Extension Manager in SketchUp (click the red gem in the toolbar)
Click "Extensions" in the top toolbar, then "Send Model to LightStanza"
Enter your LightStanza login information in the popup, and click "send"
Please note that:
LightStanza does not support separate materials on the front and back faces of a polygon. For best performance, we recommend assigning the same material to both sides. Otherwise, the extension will try to use the front-face material for export, but this can sometimes fail.
Layers are not currently supported through the extension