When you drag your Today Stack out, you will see the above stack appear on your page.
There are no contents within the stack itself that you need to edit.
You can define a static date, change the Locale, add a link, override the Timezone in the stack settings. You can also change the theme, size and the color of the top.
You can not preview this stack in Rapidweaver or in a local browser, you need to publish the page and check it online. For an summary of the remaining settings please refer to the Today Settings section.