To install a SketchUp Ruby plugin script with the .rbz format:
Select Window > Preferences (Microsoft Windows) or SketchUp > Preferences (Mac OS X). The Preferences dialog box is displayed.
Click on Extensions. The Extensions panel is displayed.
Click on the Install Extension button. The Open dialog box is displayed.
Locate the Ruby zip file to install (.rbz).
Click on the Open button. The Ruby plugin appears in the list of extensions.
More detailed instructions can be found on the SketchUp website - Here