The thanks.php content template is used to theme the content of the storefront thanks (order receipt) page.
This template file is used when located in the shopp subdirectory of your theme.
For instance, if your “My Theme” WordPress theme is located at:
Any Shopp content templates should be added to:
Some of the more general content templates have examples that can be installed in your theme, using the Content Template Starter Set. The Content Template Starter Set can be installed from your WordPress Admin by navigating to Shopp → Setup → Presentation → Theme Templates.