When you create a new FTP user it asks what the home directory should be. Depending on what you want your FTP user to be able to do, you would pick different directories. If you want that user to be able to upload web pages, you'd give them a subdirectory in /home/user_name/public_html. If you don't want what they upload to be visible to anyone on the internet, pick a subdirectory in /home/user_name/. The FTP user cannot see parent directories of the user directory, but can see all subdirectories of the user directory, so plan accordingly.
Note that file hosting is not allowed and that you are responsible for anything anyone uploads to your account, amongst other rules stated in the TOS and AUP.