When you create a new form, the default success message, upon form completion is like this:
You can easily customize the message by clicking your Form Properties tab and changing the message under Submission Confirmation.
You can also insert merge tags into the success message, to display values from your form fields.
Redirect to a custom URL
Instead of displaying the success message, you can also configure your form to redirect to any website URL upon form completion.
Select Redirect to Web Site option and then paste the URL
Make sure to enter the complete URL of the page, including the http:// or https:// part.