Well, I'm not exactly sure of what you want to accomplish, so I'll show you two different ways depending on what you want to do...
if you want to redirect to a URL, you can use this method. For this to work, you can not have sent anything to the browser yet. No echos or prints.
if ($variable==variable){
header("Location: http://yourserver.com/pagetogoto.html");
exit;
}
if you just want to include another page in the page you are doing the if statement on, then do this:
if ($variable==variable){
include('/path/to/somefile.html');
}