The vast majority of magic in Elstren is essentially the result of of 3 different 'energies': Arcane, Astral, and Faith.

Arcane energy is the magic flowing through the Cosmic Clockwork at any given moment. It is, at its most basic, the glue that holds the universe--together arcane energy defines the laws of physics and 'regulates' the universe to behave in the way that it does. People can engage with this energy through various means; spellcasters use the Supernal Dialogue, essentially an eldritch language, to command it through verbal or ritual means. Cantrip casters develop the skill to feel ambient arcane energy and command it directly without the use of this language, though with far greater difficulty, and with lower potential. In both cases, the caster uses their soul as a 'magical catalyst', drawing energy through themselves, shaping it to their will, and then releasing it to do what the caster desires.

This is how almost all magic works on Elstren. Most magic-related energies on Elstren respond heavily to will or intellect; it is clear arcane magic was created as a means of shaping universes by far higher beings, the paint that would eventually decorate their cosmic canvases, and its use by mortals reflects this intention.

Arcane energy can do anything. A sufficiently powerful spell could simply delete the universe; an adage among wizards is that the spell to unmake the world itself is but thirteen words long. Making it actually do these things is another matter--a person can only cast a spell as powerful as their body can handle. A person's body gains magical tolerance over their time with magic, and casting over your own tolerance is a recipe for disaster. At best resulting in pain and suffering and at worst in permanent affliction or death, overcasting is a constant concern for mages. It can happen all at once: with his opening spell, a mage errs and speaks but one word too many, and suddenly the arm he was channeling magic into explodes. Or, it can happen gradually: after a long and hard battle, a cantrip caster simply breathes too deeply of the magic around her, and catches fire from within as it burns her soul.