Log visited URL to file¿

I need a php script that will log a visited URL to a file.

For example, if someone visits http://www.mysite.com/user.php?UserName
Then "UserName" is logged to the text file.

I'm completly new to php so I don't even know the term to search for regarding the question mark in the URL (if that makes sense).

Any help on this would be much appreciated
Cheers

im not totally sure on this one, but pretty sure that you cant just have www.mysite.com/user.php?userName i think you have to have www.mysite.com/user.php?something=userName

but then logging it into a database, you go like this:

<?php
mysql_connect(host, user, pass) or die("Couldnt connect to database");
mysql_select_db(database) or die("Couldnt select database");
mysql_query("INSERT INTO table SET field = '{$_GET['something']}") or die(mysql_error()); // the $_GET['something'] finds the value that something equals in the URL
?>

hope that was of some assistance