Passing information via a url

I have just started using php. I am trying to pass a parameter from one page to another via a url ie: www.mysite.com/myphp.php?param=string I am then checking the variable in the requested program, however, it isn't working. I try to evaluate its value in a if statement ie: if($param == "string") { do something; } Is there something I need to configure in php to be able to accept a variable passed via a url? By the way, I'm new to php, so please be specific with answers. Thanks Adam