In the Host field, put the URL of a user's site. It has format: http://example.com/ and has to end with a slash. This URL has to be resolved and accessible on the SiteStudio box. e.g.:
In the Server field, put an FTP server of the site you are going to build. Usually it is a domain name of a client's site or something like ftp.example.com
The FTP connection to this server has to be available from the SiteStudio box.
It can be IP or domain name of the server where the client's site is hosted (depends on FTP server configuration). If the client's site is hosted on the same server with SiteStudio, it can be 127.0.0.1 or localhost.