The Thermen theme is fully compatible with the Breadcrumbs NavXT plugin. If you want to show breadcrumbs in your theme this is the plugin you'll need:
After installing and activating the plugin there is nothing you need to do. It will automatically be displayed right under the page header area on every single page.
And for customization a new panel "Breadcrumbs" is added to the theme customizer under Appearance -> Customize