Just read this great little book. It is free, in various formats, at archive.org. This is how the book starts:
The mind of man is conscious and subconscious, objective and subjective, external and internal.
The conscious mind acts, the subconscious reacts; the conscious mind produces the impression, the sub conscious produces the expression; the conscious mind determines what is to be done, the subconscious supplies the mental material and the necessary power.
The subconscious mind is the great within — an inner mental world from which all things proceed that appear in the being of man.
The conscious mind is the mind of action, the subconscious mind is the mind of reaction, but every subconscious reaction is invariably the direct result of a corresponding conscious action.
Every conscious action produces an impression upon the subconscious and every subconscious reaction produces an expression in the personality.