While it is (nearly) universally agreed among the various philosophies and surviving religions that the animating spark in all intelligent beings is a spirit or soul; the question of where this spark comes from and where it goes to, that is a matter fiercely debated.
It is known that their are heavens and hells and the Shadowed Lands between life and death, but the higher and lower realms have been sealed off since the Gods War, it is not known if souls can travel there but it is expected that they can . . . with great difficulty, especially if they wish to ascend. (Summoning beings from either can also be done, also with great difficulty.)
Back in the age of the gods, it is said that their divine magic could bring the dead back from . . . wherever it was their spirit went after it left the body. In the age following the Sundering, the dead tend to stay dead, only the most powerful magics can bring a spirit back across the veil and even then only if hours, or at most a day, has elapsed. Except for the dragonkine, once a dragon is killed, they are dead, no magic will bring them back . . . this makes some dragons exceptional cautious, others risk takers, but most just ignore it as they do not expect to die.
Some spirits linger as ghosts or more destructive spiritual beings, haunting the site of their death is the most usual place for such spirits to be found but sometimes it is not so simple and they are bound to other places, items or even, other people. Lingering spirits come in a wide variety of types, not all of which are hostile, which have lead to the development of specialized spirit hunters among many cultures such as the Ghostchasers of Taren Kost.
Of course the true secrets of life and death remain that.
Notes: Image Ghosts appearing to a young man; their names are given to him by a wizard. Engraving by B. Winkles after J. Salmon. Wellcome Collection. CC BY.
Sea of Stars RPG Design Journal 