Most creatures, when they die, simply pass on. Their spirit may linger near the mortal world for a short time, and may even be called back by the right magics (such as raise dead and the like), but even this is uncommon. Less frequently, a dying creature with unfinished business may find his soul trapped near the mortal world until his ghost is laid to rest or destroyed. The ghost that is created may be bound to either the place he dies or another place of great importance to him as a mortal and usually tied to his unfinished business.
What few mortals realize is that the soul, once released from the body, does not pass directly to the outer planes, or face final dissolution, or whatever else they believe ultimately happens to souls of the dead. When a soul becomes untethered from the body, it is drawn to the Pillar of Souls for a time, in preparation for its final determination and departure from the mortal world.