Populating a Field via a Querystring
You can populate a field with data from a querystring by setting the default value of a field to be the be the key of your querystring.
This will set the value of the field to whatever the key equals in the querystring in your URL.
Using data from a Submission as Querystring data in a redirect
You can create a redirect action that contains a merge tag from the form as part of the URL.