Before one begins to learn Magic, you must learn what exactly magic is. When most people say magic, they would simply be referring to miracles, seemingly impossible things made possible; this however, is only one type. There is the explainable, and the unexplainable. The Unexplainable is useless to us, especially in a tome such as this, so I will define it and then leave it to be.
The unexplainable works within something known as The Law of Divinity; it functions simply because it does, and that is all that can be said for it. Things beneath The Law of Divinity are literal miracles. That is all that can be said for them and, as miracles, it is most commonly seen in the works of divine beings: Demons, Angels, etc. However, certain individuals are able to trigger things that are "Divine", or function within The Law of Divinity.
In turn, we come to the explainable. It works under The Laws of Magic. It works within the laws of the universe, it obeys physics and it can be clearly defined and replicated. As Arthur C. Clarke put it: "Sufficiently advanced science is indistinguishable from magic", and that's all it is: advanced science.
Wizards, Mages, Sorcerers
Throughout history and culture, there are dozens if not hundreds of names for users of magic, and to most people these names are interchangeable, but each has it's own unique meaning. In order to clear up a lot of confusion that may arise, the four most common will be defined.
Magi: A Magi (Said "May-Guy") is the form of magic user that will be taught in this grimoire, and for all intents and purposes, a Magi is a "true" magic user. Magi is both the plural and singular name, and it isn't gender specific, though the terms Magus (Male specific, both plural and singular, said "May-Gus") and Magae (Female specific, both plural and singular, said "May-Gi") do exist. A Magi, despite the similarity in the name, is nothing like a Mage, as a Mage is a type of Wizard. Even though a Magi is a True Magic User, it's likely the least commonly known name for one, and this is simply due to how well we've hidden our existence from the Human Race.
Wizard: Wizards are what the media would typically consider to be a magic user, though this is a falsity. Wizardry is using the spoken word, enchantments and Magic Seals to incite spells, meaning a Wizard doesn't actually need any form of their own power to use magic, as long as they have the correct tools, though this comes with the downside of being limited by your vocabulary and your equipment. "Wizard", isn't gender specific but it typically refers to a Male, while "Witch" solely refers to a female.
Mage: A Mage is akin to a Wizard in how they use magic, except with the key difference that a Mage actually has some degree of their own power due to having a stronger soul than the average Human. It's nowhere near the average Magi in strength, or even most weaker Magi, but it's enough to give them a higher degree of control over their spells and enchantments, making them stronger, and in extreme cases, being able to alter them by small degrees on the fly. Mage isn't a gender specific term, and the plural is "Mages".
Sorcerer: A Sorcerer is actually a sort of Evocator or Summoner. Sorcery as a term defines the use of spirits and familiars to accomplish one's goals. Sorcerer isn't gender specific and the plural is Sorcerers, though a female Sorcerer can be called a Sorceress (plural is Sorceresses).
An interesting effect is, that due to their nature, a Magi can practice Magic, Wizardry and Sorcery, making them technically count as all of the above (though the boundaries between Wizard and Magi does become a tad blurred when a Magi is practicing Wizardry).
What is Magic
At a basic most level, "magic", is the application of energy through a non-physical process. This leads to two questions:
1) Where does the energy come from,
2) How is the energy is applied.
The answer to the first question is a simple one: It comes from all around us. There is a field of ambient energy that permeates literally, everything. It's a collected energy field produced by all regular forms of energy (thermal, sound, kinetic, etc.), however, the majority of the power within it comes from something known as the Casimir Vacuum Field (this will be explained later).
This energy field has constantly been forced around since it was created literally at the dawn of the universe, and since then has formed into a steady flow, almost akin to a river of energy, hence it's colloquial name "The Stream", though it's technical name is the Ambient Field (it will be referred by both names, however I will attempt to dominantly use technical language).
The second question, is where it becomes rather hard to give a straight answer. The energy within the Ambient Field is, for lack of a better word, attracted, to something within every living creature: the soul. The soul isn't some abstract idea, it's a real (albeit energetic) component of the body, of life itself.
This Soul, is what allows us to use magic. It allows our minds to connect to the Ambient Field, or, moving into more informal terms, "redirect the flow of The Stream". While the Soul is therefore the conduit through which we can draw this energy, one also needs a mind to control the process, and a body to act as a applicator.
In effect, to answer the second question: In order to apply energy in the form of magic, one needs a mind to control it, a body focus it, and a soul to generate it.