Hi Regis,
iTunes allows you to import and export documents via USB, but synchronization is not possible; this has nothing to do with Notebooks, it is simply not supported by iTunes.
To use import/export, please first enable this option in Notebooks' settings.
To export, select "Export to iTunes" from a book's context menu or a document's action menu.
To import, first transfer the documents to Notebooks through iTunes and then select "Import from iTunes" from the context menu of Notebooks' top level book.
You find a more detailed guideline in the handbook (p.27), which is available here: http://www.notebooksapp.com/Download.html
I hope this helps.