Actually, it's not "internal.php3?=whatever" but rather
"internal.php3?name=whatever."
If you look at the top of this page, you'll see:
http://www.phpbuilder.com/forum/read.php3?num=2&id=129235&thread=129235
In each case, after the question mark, there are one or more name=value pairs. If more than one, the pairs are separated by ampersands.
If you will read the first part of the PHP manual, it explains that PHP takes that information and creates variables that contain the values that were passed in the URL. So, internal.php3?name=whatever creates a variable "$name," and if you take its value, it will be "whatever."
When you write a PHP script, you simply use language constructs such as "if" and "else" to allow the variables to determine alternative behavior.