In a URL, everything after the hostname is a resource specification. You're basically asking the web server at 'www.myname.com' for the resource called 'hello'.
The definition of resource depends on your webserver configuration, and can be influenced by your OS.
'hello' could be a file, or a directory, or invocation of code that provides output related to 'hello'.
Using filename extensions such as '.html' or '.htm', etc. are used to provide a hint at the type of content to expect when you request a resource with that extension. Typically, 'hello.html' would be a file somewhere that your web browser can locate/read whereupon it will send that file to you. But, 'hello.html' could still be a directory or code that produces the appropriate output.
It's not generally possible to determine how the resource is implemented without having access to the web server and its configuration, but then, you don't normally need to care about that as a user of the resource.