Slates are like a book, that can have many chapters which we call Tablets. You can create multiple Slates in Facebook, each with a different title or category, and then within each Slate you can create many Tablets with the content of your documents. Below you can see an illustration of one slate named "Slate User's Guide" with three Tablets.

Slates in Preview Mode

Tablets can display photos, formatted text, links, and pretty much anything else you can have on a web page. In fact, the web page you're looking at right now is created with Slates.

You can toggle back and forth between "Preview Mode" and "Edit Mode" which allow you to view the Slate as visitors will see it, or display the editing tools available to authorized editors.  Look for the following tool bar at the very top of your web page:

Toggling between Edit Mode and Preview Mode