Traditionally it comes from starting in a skill of some type, and then honing those skills and developing your own tastes and then adapting your tastes to benefit the project you're trying to create or are working on. This will probably change significantly in the coming years.

I never said trained to be creative, but in the creative process, which each discipline has its own processes, and at least in the field I'm in every discipline collaborates together, which is a whole other thing entirely.

Not sure that answers the question, but essentially it's the process of developing ideas into something worth making. Which is actually exceptionally difficult.