URL with no file name?

[gibberish3ll3]

hi all,

I'm not sure where to ask this question, so I'm trying in this WD's lounge. Hopefully, someone can lead me to a right direction...

I started learning about XHTML and the more I look at people's sites written in XHTML, the more I realize that their URL does not contain a file name. Traditionally, the url contains a path to some kind of file (ex: http://www.domainname.com/folder/index.php). But those sites that I've seen do not contain any file names in URL or links (ex: http://www.domainname.com/folder/). How is this done, and how does this work???

I'd really appreciate it if someone can point me to an article about this or tutorial. I'm just curious how this is done.

Best Regards,
gibb