The Showcase Template is aimed for use as the home page of your site (if you choose to use it…that’s the key…you must choose to use that template…otherwise you won’t see that widget you mentioned).
So, go to the page you are using as your landing/home page and off to the right you should see a box titled Page Attributes. There is dropdown menu that allows you to choose a Parent for a page (this, I’ll guess, is your home page so there is no parent) and there is a dropdown that allows you to choose the Template you want for that page. Select Showcase Template and update. Now you should see that widget you mentioned.