It is not a secret at all, and I say this because I learned from scratch using nothing but the official documentation and video/written tutorials. There is a bit of a learning curve, but once you have the fundamentals down you can make whatever you want.
Important links, here you will find documentation and videos for reference:
.unrealengine.com/latest/INT/
Here are some recommended tutorials, follow along in UE4 as you watch the video (pause it if necessary)
https://wiki.unrealengine.com/Videos?category=Basics
https://wiki.unrealengine.com/Videos?category=Blueprints
https://wiki.unrealengine.com/Videos?category=Build%20a%20Game
I guarantee you after watching and following along (it’s critical you do this, you learn by doing) that you will be able to start designing your own games and experimenting with different game mechanics. A couple of the video series in the links above take you through the steps needed to build an entire game.
Really hope that helps, and remember it may seem confusing at first, but stick with it! It won’t take long before it all makes sense. 