This plugin serves to integrate the editor with an external file manager (an application that provides file browse/upload capabilities). It defines the protocol to associate the file manager application with any dialog window field that has a "filebrowser" property in its dialog definition.
Note: This plugin is only responsible for the communication between CKEditor and an external file manager. You need to either connect a custom file manager that uses an appropriate API, or use a ready to use file manager compatible with CKEditor like CKFinder.
This is an official plugin provided and supported by CKEditor developers.