It looks like it is using $_POST but your form is using method="get"
Try updating line 21 from:
$WADbSearch1->keywordComparison($KeyArr1,"".((isset($_POST["courseDescription"]))?$_POST["courseDescription"]:"") ."","OR","Includes","%20AND%20","%20OR%20","%22","%22",0);
to:
$WADbSearch1->keywordComparison($KeyArr1,"".((isset($_GET["courseDescription"]))?$_GET["courseDescription"]:"") ."","OR","Includes","%20AND%20","%20OR%20","%22","%22",0);