Where does magic comes from?

It's the memetic reverberations of a greater set of powers and beings repeated through incantation to achieve desired effect and outcome because it's a force that touches upon all observable forms of matter through proxies.

Basically, think of it as a universal debug code, the game engine is the reality and the rules it is in and the spells are running commands through crude amateur methods. Truth be told, the most important thing about magic is to discover how to make it from scratch so the miracles it brings last forever.

It's basically cheating, but in a more significant fashion

Inspirado

It doesn't come. It was there first.

Gold. Gold is magic solidified.

An emanation of God.

The Warp.

The soul

Finnish memes.
Ancient finnish memes.

Does that mean that gingers can't use magic?

Every living thing , a lot of created things that can almost be called living, and several dozen non-living things have a set of "organs"/circuits that interact with the otherwise-parallel plane of raw power.
A practitioner can become stronger by exercising magic, and enchanted items are created by inscribing them with the proper magical circuitry to get the desired effect.

Magic is the imposition of thought so strongly that it overrides the world around you. To make this work, mental energy must be expended as fuel.

This isn't as simple as just making yourself tired. If you burn a piece of paper, you don't get more paper by letting the sheet sit and rest. The burnt paper is gone. Forever.

Thus, while it is certainly possible to burn your own memories for fuel, its only ever done in the direst of need. Especially since you can never precisely control what memories you will burn.

Instead, wizards draw on outside sources of memories. The most common is to invoke elemental spirits. As immortal beings, their memories stretch for eons and losing some small amount of them is of little consequence.

Necromancers steal memories from the dead. Many see this practice as obscene, as it has never been conclusively proven whether this degrades the soul of the dead and affects that individual in whatever afterlife exists beyond the grave.

In general, mages carry around flasks of oil for fueling spells. Fossil fuels are made up of thousands to millions of ancient dead, mostly animals. Individually these animals would have provided a trivial amount of magic in life, being of incredibly simple mind, but together in the form of oil they add up to a rather potent source of magical energy. Using oil for magic renders the oil 'exhausted', though exhausted oil still burns for the purpose of mundane fire.

as far as i have understood it so is magic something a bit like a "hidden layer", almost as a sort of primordial form of electrical charge, that exists within everything to a certain degree. most of the time this is explained as the background radiation from the gods or whatever beings that created the world. because it's leftover gunk from "the creation" so does it have some of that creation property left, and can thus do anything, as long as there is enough, handled with enough skill

wizards can learn to manipulate this with a lot of study.
the sorcerer is pretty much already a "node" full of the stuff, but needs to learn how to harness it.
the bards singing/music is somehow reminiscent to the creation of the world, and the magic reacts to this.
the cleric's bond to deities are making "echoes"that they can manipulate. sometimes directly for the god, most of the time just from being "close" to a being that is radiating this power.
druids got a direct bond to life itself, which is a very potent "conductor" of magic. similar to the clerics divine bond.

and so on

The powerful will of Bolshevik unity and the socialist revolution! Or severe brain damage from an artillery blast awakening hidden powers in a young Neosoviet nurse. Spooky.

Magic isn't a force, its a skill set. Any "wizard" that talks about mana or spiritual energy that fuels their spells is nothing more than a backalley con man, making excuses for why he can only perform his tricks for you once before you give him another few minutes to shove something back up his sleeve.

Its true that a magus can tire themselves from using magic, but that's the result of their own stamina and nothing more.

You either know the secret name of fire, or you don't. Wizards don't refrain from invoking these powers because of a limit resource, they refrain from abusing them because invoking Words like that is fucking dangerous.

The greatest pyromancer I ever met in my studies had no legs and was scarred on more than half of his body. All of that was self inflicted. Thinking you are ever really in control of the forces you call upon is the surest way to find out how little your commands really mean.