We've got them where I'm from. I'm guessing methods of handling them might be different, but the basics: Spirits that either have unfinished business or, more commonly, are just really really pissed off, assuming they're sentient. The latter's the only kind I've ever actually seen. So if there's a ghost, there's a trail I can follow to find out why they're a ghost.
I could tell you how to handle my world's ghosts, but unless your world's ghosts respond to magic and healing items, I don't think it would do any good. That and I don't have any potions. Knew I should've gone into town for stuff before that fishing trip.