Sound of Magic

normal spellcasting in mutania

Magic in Mutania isn't a nebulous concept or something contained within books: it is the effect of specific sounds that vibrate astral particles and the intention of the spellcaster to cast magic. While the intention to cast magic is required, the exact intention of the spellcaster can be muddled by their execution.
Magic can be applied to external objects and the spellcaster's own body. Because magic is the result of astral particles, it is always accessible to the spellcaster, but infusing the body with too much magic can result in a magician becoming headspun, which can become a serious condition that reduces their ability to convey their magical intention, weakening their magic forever.

Manifestation

Astral particles in the air are not visible to the naked eye, but they exist all around the normal matter of the world. They exist in a semi-separate plane called the astral plane, and it is this plane that serves as a connection point between a binary set of universes. Mutania exists in one. There is another universe out there, one alien to the people of Mutania, that is intimately linked with the world they know.
To perform spells, one must activate the astral particles, which are responsive to sound waves. Some spells require a simple snap and others require convoluted passages of texts in specific languages. These astral particles move according to the spellcaster's intention to do magic. Someone can snap their fingers and not have something explode, but a magician who messes up a spell can accidentally cause a lot of damage if their magical intention is not aligned with the sounds they create.
While magic is a normal part of every day life and can affect many things, there are some things that sound/astral-based magic cannot do. It cannot be used for necromancy in any form, nor can it be used to affect the mind of another in order to coerce specific actions or feelings, thus one cannot do magic to make someone fall in love or to harm themselves.

Localization

There are other forms of magic that are not sound/astral-based magic, such as river magic found in the north by the Veins. That magic is granted to spellcasters by the power of a river's spirit, called a zibeke. River magic actually does grant a Veinlord the power of necromancy, over both large groups of animals and individual sapient entities.