Ok lets take your example. This is what goes on:
1- in the roster section of http://cs-eagle.com/roster.php they create a list of members with a link to their respective profiles like this:
<a href="http://cs-eagle.com/roster.php?roster_id=65">Profile</a>
2-When you click the profile link you are taken to the same page with a modified query string. It then reruns the script validating the query string and using a conditional statement by using something like this:
$pattern = "/^\_id\=/";
$id = preg_replace($pattern, "", $_SERVER['QUERY_STRING']);
if(strlen($id) <= 2) //this is a tribal way to check that preg_replace() returned a 2 character/digit string/number.
{
//pull profile from db for the corresponding member $id
//display
}
else
{
//list all member names and profile links
}