Slate and UMG - What's the difference and how do I find UMG documentation?

It seems there is little to no UMG documentation, but tons of Slate. From what I’ve gathered, Slate was there first and UMG is built on it, but Slate is still used in C++ implementations, while UMG is the new “Widget Blueprints”? Let me know if I’m on the right track guys – very confused!

Thanks!

And watch the latest Twitch livestream as it was covering UMG and might answer more questions. Basically UMG is a visual interface for using slate.