I am studying php routing material now, but I still can't understand the theory. Does anyone here have good tutorials or links to share?
You are talking about url rewriting, and there are many other questions about that on here if you search for that term.
Regardless, url rewriting isn't handled by PHP, it's done by the web server. If you are running PHP under Apache, then you'll want to have a look at mod_rewrite. For IIS, you would look into the IIS Rewrite module (which conveniently can import mod_rewrite rules from apache as well)