The old bedsheet and chain

When something goes bump in the night, it usually not the Bogeyman (sneaky bastards that they are) but infact ghosts.
Ghosts are a breed on to themselves and pretty unique in the supernatural scheme of things. The best way to explain a ghost is to think of them as an echo, shadow or footprint of a living persons soul. Ghosts that are actually sentient remanents of a persons soul are extremely rare.
Most are just a piece of a persons soul, that left a mark upon death. Due to trauma, stress, sadness, fright, anger or hate. The stronger the emotion, the greater the chance of a "impression" being made.
So the ghost isn't the real person, The ghost is more like a copy made of spirit energy and there are no desernable rules for the way a persons death creates a ghost.
Some claim that people with magical talent make ghosts when they die, but then there'd be a shitload of mage ghosts around and there ain't, so that's one theory out the window in my oppinion.
The ghost is by no way an exsact copy of the deceased person, most are just scattered fragments, repeating patterns or specific actions. Moving things or making noises, your typical poltergiests. 
Others are more coherent and will appear as translucent shapes or bodies, following specific paths. But unaware of their surroundings.
Some ghosts might be such strong impressions that they are aware of their surroundings and can act with them. These are your typical hauntings, relatively harmless in most cases. The ghost may move stuff, make noises or appear randomly. spooky and unnerving, but ultimatly harmless.
However, this is not always the case, most people react to ghosts or in some instanses the ghosts react to them. The classical exsample is that a new family moves in and this for one reason or another "wakes" the ghost. where it before just misplaced the occational book or shifted stuff in the drawers or made the roof creak. Something will trigger it and it will lash out at the family.
Don't look for reason in a ghosts actions, they arn't sentient, like you and me. More like frayed patchwork of personality, with some stitched on random thoughts and occational feelings. it's doubtful they even perceive the world like we do.
So a Ghost may lash out seemingly at random or stalk one particular person, or strike at a person or people for a specific reason. I once helped exorcise a ghost that tore the hair of girls at a school, if they had long hair and wore it loose on sundays.
Also, A ghost is bound to something. it's impression is imprinted on something. usually a place, but a thing can also be haunted, the ghost follow it.

The trouble here is, if a Ghosts has enough presense to lash out, it's usually powerful enough an entity to do some damage. ranging from knocking stuff and people around and tossing things at them, not really lethal unless it shoves you down a stair. To tearing at you, breaking limps, tossing people and furniture around. To Ghosts so powerful they can warp their surroundings, litterally turning you're surrounding against you. Ghost possessed Earthmover, bad news, take my word for it.

So, how do we deal with ghosts you ask.
There's some simple facts and rules. First up, the bad news; Ghosts are already dead, so you can't kill them. but despair not, there's plenty of other possibilities.
Ghosts are either incoporeal or coporeal, meaning that they are invisible without form, meaning you can't see or harm them. but on the bright side, they can't hurt you either.
To affect you, a ghost needs to take form, it might still be invisible, but there are ways around that.
There's spells that will show ghosts and they show up on photos, cameras, dogs and cats sense them to (but can't really point) Be aware, that a ghost is strongest when it's corporal and visible, so when you can see it is when you have to be most careful.
A ghost, when it has taken coporeal form and affecting their surrounds will often turn the immedeat area cold, a handy headsup if they're still invisible.
Ghosts possessing something or moving stuff around for a longer periode of time will leave a residue of ectoplasma (magical byproduct, sort of a universal spirit go) it evaporates after a few minuts without trace.
Being composed of spirit energy, a form of magic. Ghosts affect electrical circutes, so their presents can sometimes be heralded by flickering lights and tvs going on the frizz (some hunters rigup little scanners that pick up the interferance, but I'm not tech savy enough for that)
Being spirits, Ghosts aren't fond of Iron and salt, it tears up their form and depending on how good you got them, it'll take a while for them to get themselves together and come at you again. anything blessed by a holy person will work fine too. Supernatural, tvshow with two brothers hunting otherworldly stuff (most things in it are totally off the gird, but some they do get right) shotgun shells with salt, works wonders, if it plays merry hell with the wall paper and be careful with friendly fire. bad enough to be shot, but with salt? That'll ruin your weekend.
A ghost cannot escape a closed iron container or a closed cirkle of salt. Binding cirkles can also lock them in or out.
Destroying or exsorcising a ghost is trickier: if you can get hold of something of the person body; hair, teeth, bone or close personal belonging, such as favorit necklass, glasses, jockstrap (true, if smelly story) or dog tags. There's rituals for banishing a ghost, even non mages should be able to manage. But depending on the strength of the ghost, you might only piss it off.
If you can find the burial place of the ghost how ever, you exhume the remains, salt them, burn them and douse them with holy water (not nessasary in that order) That'll take care of any Ghost.

Ofcause, such extrems arn't always nessasery. Ghosts of that magnitude tend to have left an impression for a reason, either they died something unfinished or never done, or were wronged. Finish the job, do the deed or rigth the wrong and the ghost will calm right down and go back to knock on walls or even dissolve altogher.
Ofcause, with ghosts nothing is absolute, seeing as they are copies of people and as such don't make sense either. So some ghost might just carry on their haunting or even step it up a bit. It's rare, but don't let you guard down right away.

Finally, true Ghosts. not that the others were false, but some rare ghosts, are perfect copies of peoples souls and actually think they are the dead person. (being a copy they, for all intent and purpose, are) and act accordingly, there's even been records of ghosts not realizing they were dead or trying to keep on living their life after they died.
These are easier to deal with if you can reason with them, but far more dangerous if they get pisssed off.

So, to sum up. Most ghosts you barely notice are there, and if you do, most are just a little spooky. But if they go all "Ringu" on you, be on your toes and don't think you're safe just cause you got your back against the wall.