Your conscious mind is what you use whenever you are awake and need to create new patterns, your unconscious runs those patterns and works with the feedback loop of the chemical body.
So what does the subconscious do?
The subconscious mind is the part of you that looks after you and cares for you deeply. When the conscious mind is not aware, the subconscious takes over. When driving, you may find that you arrive at a destination without realising it or remembering how you got there. The subconscious has taken care of this for you.
Subconscious is like a librarian for the patterns and processes that the unconscious runs. It can also change the patterns are needs require those changes.
The common view of the Conscious/Subconscious relationship is an iceberg, where the conscious mind is the bit you see above the water and the subconscious is the bigger part below the surface.