you are just using the variables in those lines, there needs to be code before those lines that assigns those variables values.
For example, the booking date is comprised of three select lists named "Month", "Day" and "Year"
you need to add code to create the $sBookDate variable using the three select lists:
$sBookDate = "".isset($_POST["Month"]))?$_POST["Month"]:""."/".isset($_POST["Day"]))?$_POST["Day"]:""."/".isset($_POST["Year"]))?$_POST["Year"]:""."";