The number isnt the URL - what this does is call a page "link.php" and then sets the value of the variable "$id" to one, so that the programmer can make use it in in his page.
For example:
if i had a page "index.php", which had somehthing like;
<?php
echo "<p>Hello, ".$name.", and welcome.</p>";
echo "<p>You are ".$age." years old.</p>";
?>
Then if I gave you a link to "index.php?name=John&age=22" then the page would insert the values that i've given for name and age (namely John and 22) into the page it generates. of course, you can then get a lot more complicated and do various things with the values you are give, or even get a page to do completely different things depending on what variable values it's passed - but you get the idea.
Does that make it any clearer?
