Login to your computer as an administrator to assure the extension files get installed into the proper locations with proper ownerships and properties.
Launch SketchUp.
Open the SketchUp Extension Manager control panel.
Window > Extension Manager
Click the Install Extension button.
Locate, select, and open the RBZ extension file you downloaded earlier.
Enable the extension.
Close the SketchUp Extension Manager dialog panel.
The extension can now be launched from the SketchUp Extensions menu.