Imagine your standard old word document screen. Now imagine that instead of typing line by line, you can click and type anywhere on the page...kind of like making a series of lists on a piece of blank paper.
Then you can layer it as well. Say for instance I"m taking this summer class. I want to keep all my notes for class in one file. I'll have a layer for notes from one of my textbooks, a layer for notes from the other textbook, and a layer for notes from the lecture. They're all tabbed off on the right.
Tabbed at the top then are all my different documents--class notes, to-do lists, etc. It's like being able to have open a dozen more versatile word documents at the same time, all accessible by a single click. It's really pretty innovative.