If you can't see your Skype ID in the plugin's window (as in the picture below), most probably you are using a version of Skype other than Classic Skype. (Please note that the plugin is compatible only with the Classic Skype version).

If your Skype looks like the one shown in the image below, you have to uninstall it from your computer and install Classic Skype from this site: http://download.skyprivate.com/skype/win/SkypeSetupFull.exe