[Plugin: FormBuilder] how to retrieve the field value?

Hi,
Thank you for the good plugin of FormBuilder.

I am developing 2-page form.

Please let me know how to retrieve the field value at an alternate page.

When I tried a code of
<?php
$posted = $_POST;
print_r($posted);
?>

only NULL appeared.

http://ww.wp.xz.cn/extend/plugins/formbuilder/