How would you set up the files and folders on an FTP server so that
typing in a URL such as www.domain.com/other will go to a webpage
rather than to a page fault?  So that people don't have to type in
/other/index.htm

This feature is controlled by the configuration files of the webserver.
The administrator, of the server may change the name of this file to
any or many different names and extensions, in the servers
configuration file.

Apache Webservers by default, will display this first page of index.html
Microsoft Webservers by default, will display this first page of default.htm

The user or uploader of files, just needs to know what this "start"
html page is named.  Then upload the index.html or default.html to the
directories you create and it will display the page. New directories
by default use the same start page name, as the home directory.

FTP sites by default display a folders contents.

Let me so I may elaborate further, or provide live examples on my webspace.

Thanks for the question,
Jason.

Thanks Jason.  That's fixed the problem.
dhrs-ga