Are you looking to pass value(s) that a visitor submitted in on one form into another form? You are in luck! With Forms, you can do this by passing the values through the redirect URL from the first form.
Sample Use Case
If you are requesting that a site visitor complete a form that contains multiple Forms pages you are going to want to make sure to retain the individual's contact information from form to form so that you can tie them together.
To do this, simply pass a unique identifier field value such as the visitor's email address from form 1 to form 2.
You can even make the field on the second form hidden so the visitor doesn't see the value being passed. For testing however, I would make sure to keep the field that is accepting the passed value visible on the form so that you can make sure it is working and the value is being passed successfully.
Syntax
For this to work, make sure your redirect URL uses the following syntax:
http://www.yoururlhere.org/form-2?API_name_of_field_you_want_to_fill_in_on_form2={$API_name_of_field_on_form1_to_be_passed}