A ghost is always directly a dead human while a demon is a fallen Angel who lives in a higher dimension. Although some evil humans are directly invited to join the demons, and many Angels may in fact be dead humans.
Ghosts are generally harmless, and display themselves in visual, auditory, and olfactory ways. Demons on the other hand are deeply dangerous, and can physically hurt people, or even possess their minds, and bodies.
If a demon sees me and I see it will it hunt me?
(Serious question)
Yes if you make direct eye contact with a demon in any form then he will hunt, haunt, and try to possess you. If you did look into his eyes then you must seek the help of a demonologist to cut the ties of evil.