The redactor is a simple light weight richtext editor that comes with and OEM license with DG3. That is, you can use this one in you DG3 application, but it is not free to use anywhere else. A basic integration with fileupload module is created. You can use it by adding the following urls to your richtext field. 

Browse /_upload/redactorimagebrowse/ Browse for images listed as thumbnails
Upload /_upload/redactorimage/ Upload images by drag and drop

The field works as any other fields in DG3. Data is exchanged automatically with the server using ajax.