is there a document about how to use Machinery with C programming language for game development?
No, there is no guide right now, but you can have a look at the “first person” and “third person” sample projects, available from the Download tab. They show some simple examples of writing gameplay in C.
I’ve been going through the new interactive sample scene, and although I can understand some of it I don’t really quite understand certain aspects. Will you be making a guide soon for beginners? I’m mostly a 3d artist and I find the engine a bit daunting to get into. The node editor isn’t so bad (quite fun actually) but if I want to modify the interactive scene I wouldn’t really know where to begin.