What we know so far[]
The absolute fundamentals of the manipulation of magical energy are, to be blunt, very poorly explored within the story. As of writing this, those very elements are only starting to be explored so a lot of this is supposition and backtracking with new knowledge.
Magic's usages are intrinsic to the class you gain them from. A fire mage for example will be able to select from an enormous list of spells as they level up and are able to utilize each of them immediately after. Magic gets interesting in two ways: one, is that there is a huge variety of magics, scrying, dust magic, silver magic, blood magic, weather magic or void magic to mention some. Literally any concept or physical object can be a school of magic.
As we're learning with the new chapters, by training your ability to manipulate mana you can increase what you can notice from the magic around you should you be able to see it, as Ilea noticed more defined details in how her friend Maro used his death magic after she started training for the first time in magic manipulation using a gift called the armor of trials to notice how her mana traveled under the armor's effects. This most likely means there are far-reaching applications of magic beyond what the class you gain would imply that you can access should you have a formal education in mystical knowledge.
Magic seems to be a fundamental part of the world of Elos. Magic even goes so far as to determine how creatures can evolve and grow, as the more dangerous and powerful monsters tend to only be able to live in mana-rich environments like those in the northern regions. This allows weaker species like Dark ones to feynor and even humans to be able to live in a relative but fragile peace on the outskirts or hidden areas in less mana-rich environments. A somewhat unique part of Azarinth healer is how magical ability seems to hinge so completely on race. Sapient races from demons to Dark ones seem to even without ordinary classes come born with naturally less powerful magics than what pure monsters are born with. Dark ones simply being enlightened monsters are affected the least by this fact but it remains constant. One thing to further cement this point is actually in the beginning of the book, as with Ilea's mutation into an Azarinth healer she gains an increase in natural mana regeneration and overall power that seems to be one of the absolute best gains among human/all the other races that apply for it, classes.
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Another notable trait of magic is that seems to have 'related elements'. The dark one Goliath Ilea met noted the relation that her element, ash, had to the concept of death. Similarly to how Ilea can summon heat and fire despite the fact her element technically is just the remains of a burnt object, it could be believed that a magical element can summon forth not simply the element alone, but all of the 'related concepts/materials' that construct the element. In essence magic can possibly operate by 'cheating' a bit, ex: you can summon 'corrosion' magic. Acid and gas could be elements of that and come as 'related elements'.
Runes[]
Runes are a language that through which one can enact and utilize magic of seemingly near any type they want because the rune holds the 'knowledge' of the magic. But as recently shown simply trying to read a rune without a enchanter class can mean anything from instant death to an ungodly headache if you are below level 200 or even a bit above it. The knowledge a rune holds is not something meant for those incapable of handling it, as similar to how Dark ones share the 'memory' of how the faeries saved their race it isn't simply facts and typed words but concepts and metaphysical understanding that if you lack the mental capacity both in a physical and magical sense to reconcile with, it will mean your death. As a caveat, someone like Ilea would most likely be absolutely fine learning even the most advanced of runic knowledge as on top of her extremely high level, both of her classes are not only very elite but one of them seems to connected directly to arcane power, meaning her ability to withstand lovecraftian hyper-knowledge of the universe should be very high.