First create your ShareProgress page, then paste that URL as your "After-Action Redirect URL" in NGP.
After you create a page on ShareProgress, you will receive a url for your newly-created share page. Highlight this url and copy it on to your clipboard.
With that URL copied, go to step 3 of the Form Creation workflow (Confirmation & Deactivation Messages). Enter in the URL under the "Specify an external Thank You page URL":
Don't forget to publish your form!