New user can browse whole MyCloud

I would like to let him see only my public and jis own user folders.
Now as I added new one, he can connect via FTP and go wherever he wants.
Any way I can limit his access?

You should read the My Cloud User Manual ( if you haven’t already. In particular Chapters 6 Users and Chapter 7 Shares, which detail how to setup Users, Shares and how to set to Shares to Private and grant User access (No Access, Read Only, Full Access) to that Share.

Note that if one sets the Media Serving option on a Share to On, any DLNA client will be able to access the media within that Share regardless of the Private or Public setting.

One can disable FTP through the Dashboard > Settings page.