If you have SketchUp v8 > M2 [and v8M5 is the newest... so you probably do !] - or ANY v2013 etc... the Preferences > Extensions > Install... button takes a chosen plugin's RBZ archive and installs it for you into the main Plugins folder - without the need for you to wear out any brain cells pondering what to do with it... If you have >=v8M2... and also have the SketchUcation PluginStore Toolset installed, then its dialog will let you AutoInstall Plugins/Extensions directly into SketchUp without even downloading the RBZ... And... unlike the native installer... it also allows you to install into your own custom-plugins folders... It also has an Archive Installer [run off the menu] to auto-install the few plugins that come as RBZ/ZIP archives which are not directly listed in the very comprehensive PluginStore database... and also other useful tools like its Plugins and Extensions Managers, its Plugins-Uninstaller etc... So... well worth a little research on SCF...