Well, this isn't a scary story but an explanation. It is to clear the name of ghosts that are good. Only the good ones. I can tell you about bad ones, but at a later date.

No ghost appears at will. Most are forced to day in and day out, in their haunting memory.

If someone is murdered, and they are innocent, they will come back and seek revenge. The reasons for ghosts is that when someone dies, they come back as an spirit, maybe a spitting image of the person they were. They are close to vampires except all vampires are cursed to torment, pain and evil. Vampires use their actual body, but ghosts do not.

A ghost will come back if they...
love thier home and refuse to leave
were murdered
want to kill(but that is evil, no worries)
And many other reasons.

Ghosts are the basic imprint of the spirit and are a constant reminder of death lurking in every corner. People may not respect them, but they simply dead people who wished to stay. If you respect your lost loved ones, you should respect every ghost that comes your way. If you were to die and to come back, you would want respect. There is much more complicated stuff and i have not even scratched the surface, but where ever you go, just remember that they too, were once human.