Spirits, otherwise known as Souls, are one of the main parts of a being. To many researchers around the Realms, a being is made up of the mind, body and Soul. The mind, an alternate name for the brain, is where information is processed. It works in unison with the Soul in this job. The brain takes in the information from the source, and organizes it. The Soul will give the brain information that seems similar to the situation at hand, helping to process. If the Soul can't recognize the situation, it leaves almost all of the work up to the brain, throwing in information when it can. Once the situation has ended, the brain and Soul work together in reflecting on it. The brain passes the information to the Soul, which handles memories and power. The mind or brain is also where all of the life processes are controlled from.
Willpower, another name for Mana, is stored in the Soul, but is shared between the Soul and mind. Mana is also the form that all informtion inside the body takes. The Soul is split into different sections, dealing with different varieties of Mana such as memories or emotions. When needed, the Soul retrieves this Mana and sends it to the brain for the given purpose.
It has been theoriezed that the passage of information between the mind and Soul would produce a massive amount of energy. The near instantaneous movement of pure energy would leave behind some sort of residue. This would explain why beings with Souls can regenerate Mana and the Soulless can't.
Memories make up the largest part of a Soul, at about 60%, while emotion is about 20%, motivation and drive is about 10% and the other 10% is either empty space or extra room for other information. So far, no facility has successfully split a Soul, which would be difficult given the fact that without the "shell" of a Soul, the Mana would disperse quickly.
It is possible to create a Soul from scratch, but the process is tricky. One would need an object that closely resembles a Soul. This could be a gemstone or a glass sphere, something even slightly transparent will do. Once this is done, a body will need to be created. This is often done by summoners, simply by building a Golem. The fake Soul is then attached in some way, ideally somewhere inside the body instead of outside. Once this is done, the summoner would then force some of their own extra Mana into the body. And since Mana typically moves upward, the Mana moves to the top of the body, forming the mind. The Golem is now extremely impressionable, but is also incapable of perceiving anything that goes on. To fix this, the summoner shares their memories with the Golem, and through this the summoner has jump started the Golem to life. Now with a functional body and mind, a summoner could, in theory, create an infinite amount of Souls.