If you edit the document in your local folder, your changes will automatically be uploaded to the portal.
If you edit the document elsewhere, you can click edit on the file in the portal, and then choose your new version, that new version will then be downloaded to your local folder.
So the answer is either. Sync just uploads your local changes and downloads changes made on the portal.
Firmi prego dentro per inbandierare questo come inadeguato.