By default, logging into FTP will open the FTP root directory of your FTP account. In order for files to be publicly accessible, you will need to place them in the httpdocs folder. The httpdocs folder is the directory opened when someone accesses your domain also known as the web root directory.
If you add additional domains to your hosting account you will specify the folder to put the files for the new domain. You will be able to access this folder from the FTP root and this folder will be the web root for the new domain.
