Trailing Slash on URLs rather than file name

I am trying to make a site, such as example.com/about , where the page is after the slash without the .php or .html, like example.com/about.php

I have looked online for what this is called but I couldn't find any information as I am not entirely sure what to search.

Can I do this by having folders rather than individual files, and within those files do I need an index.html?

Thank you