You first need to download the plugin. The latest version available can be found here. 

Installing the plugin is really easy. Once you downloaded the installer, all you need to do is to execute it and follow the steps. 

Windows (RTCCplugin.msi): 

The plugin is now installed for all plugin-compatible browsers. 

Mac OS X (RTCCplugin.pkg):

The plugin is now installed for all plugin-compatible browsers.