Highlight any text in your form and click the link icon to enter your link.
Your link will appear blue and underlined, which will open in a new tab when clicked.
You can add a button to an ending page. Drag and drop the URL button to the form. To customize, click the button followed by the settings icon to open the right-hand panel.
You can even make the URL dynamic based on form inputs by clicking the + icon.
You can also link to an external page automatically, via a redirect. See ending page for details.