That's a big subject. I could leave a long post but it's too late. Needless to say, the question of the subconscious is the subject of mounds of research and thinking. It's not simple. Start with your basic psychology, touch up some philosophy- in your native language- play around with "mentalist" tools and meditation/hypnosis, and maybe than you'll begin to get an idea. But, then, you've already lost it. Elusive is the mind when you look for it, self-evident when you realize that you are it. Work from there...
KO