Understanding this difference requires seeing the mind as a pyramid of information levels, from physical neural interactions to thoughts.
How does a level of information form? It relies on a group of neurons receiving simultaneous arousals. They codify the regularities by the signals that their own axons emit to other neurons. The code is based on the position of each neuron within the network (graph theory). The "speech" of each neural group shows some stability (neighbouring sets of arousals trigger the same response). But it evolves easily by pruning or creating new bonds. Very active phenomenon in the child's brain.
Each level of information has relative independence. The stability of neural discourse is the basis of intent. As the same "word" is triggered for different nearby sets of stimuli, it can be said that it seeks itself in sensory signals. The mind thus builds its reality.
The complexity of neural codification increases as successive levels overstay their information on previous ones. They incorporate an increasing number of criteria. The pinnacle of this integration is conscious space, a network scattered throughout the entire brain. It is kept awake by the influx of sensory stimuli and by exccitator nuclei active during the daytime.
The independence between levels of information is relative. The synthesis performed by the upper level retro-controls the activity of the lower level, without upsetting it, otherwise the mind would be a random chaos. The greater the distance between two levels (in terms of complex flooring), the less the upper level intervenes directly on the lower level.
You now have the organization of the mind before your eyes. In this pyramid, the conscious top retro-controls the immediately underlying contents. We are aware of what constitutes our thinking and may seek to change it. It's the subconscious.
While it is impossible for consciousness to directly access the base of the pyramid, for example the organization of retinal stimuli into visual objects. This is the unconscious.
Inaccessible? Not completely. Conscious intent can influence subconscious levels that are effectors on the unconscious. This is the basis of the placebo and nocebo effects, a source of very real metabolic changes.