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.
Pre-selection a list item via a querystring
To accomplish this, the key needs to be the field key for the list and the value needs to be one of the list values.
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.