Tom Smith might be smith. In some cases where duplicates arise, we use something different. This sets up the path to each student's separate site. We usually use this same name for your username for student sites. At other web sites, other conventions are followed.
Every web server has a setting for something called the site index page.
For the course site server, for example, its default.html. This is the file name the server will assume holds your home page. It is the page the server will send to someone who sends a URL without specifying the file. This means you should build your site around this page. On other servers in the world other index page names are used.