Using Wordpress like Amplify dot com

Anyone can help...
I was suprised when I knew that are using Wordpress MU. I really interested about that and until now I still try to learn how to make it.
Can give me a clue about that? Or, where I can learn about using Wordpress like that.

I mean, that's unusual wordpress used, for me. They used (maybe) some javascript or other for their user dashboard. So the user no need to see the dashboard. Like P2 theme, they can post directly at front-page. But in Amplify its more complex.

Thank you very much.

Romi Mardela