The URL structures above allow the passing of variables and values from one page to another without having to use cookies or sessions or the like. The items after the ? are simply variable and value pairs and multiple pairs can be separated by an & such as,
http://yoursite.com/page.phtml?var1=val1&var2=val2
if you were to echo the variables $var1 and $var2 using PHP in the page.phtml file, you would get... well, try it and see what happens 😉
These links aren't special to PHP, and can be used for other scripting languages as well, such as cgi/perl/etc.
Hope that helps 🙂
Tim Frank