Magic- howdy, that one's a doozy.
Before Hominids were made, Gaia had two moons. The one that remains, the Goddess of Beauty, Art, and Love: June; and her sister, the Goddess of Magic, Mystery, and The Stars: Stella.
During the time of the Empires of Vetur and Eldur, magic was exclusive to those that beseech the Gods. None could simply learn magic, so those that were lucky enough to be granted power shaped the world for themselves with great cruelty. In response to the world becoming more tyrannical and dark, Solomon, the head servitor of The Gods and primary paramour of Stella, descended.
Eventually, Zephyr shifted the wind so that Mortals could fight back against the perfection of Solomon- and the new Empire of Elementa was born. The great servitor was defeated, and the first spell outside of divinity was cast by The Great Elemental on the body of Solomon. The first necromancy.
Stella was wrathful to say the least, but unable to directly harm the mortals that slayed and dined upon the essence of her beloved Solomon. She saw their crude necromancy, and showed them what true darkness looks like. Reanimating her love, Solomon was changed into the first Devil, and went on to curse the Primordials back into submission. Gaia and Animas were forced to intervene, ending the mystery of The Gods and changing the course of mortal progress forever.
This exposition, I know, doesn't explain where magic comes from at all. Yet. Animas is not only a God of flame, craft, and strength; but is also a God of revelation. One that can divine the future. In response to a vision, Animas convinced Gaia that other vessels for the mortal spirit should be made, and she preoccupied herself with the creation of hominids whilst he drafted the Dragons.
What happened next is a matter of debate, but one thing is certain. Stella was destroyed by Animas- her own father. In a great event called The Red Sky Days the world was engulfed in the calamity of Gaia's second moon breaking into countless pieces and plummeting to the planet's surface. Gaia forevermore would be wrapped in the dark violet ring of Stella's Sundering, a permanent fixture in the sky even now called Stella.
After the Sundering, the hierarchy of The Gods was thrown into disarray. Animas was imprisoned within the roiling rage of Gaia's core, Zephyr was sent on a never-ending journey to observe mortals, and Stella was slain. Gaia was left to clean up the pieces as Flucas was a God of Knowledge, not creation. After her reorganization of the world, she considered how she would never see the Magic of Stella again; and in her grief she left Stella's essence untouched- free for the taking for all Mortals.
In the beginning, magic was wild and uncontrollable. Stellan temples were built from the stones of the moon, and the oracles in a frenzy wrote the arcane formulae for their flock before experiencing the most sublime form of Spell-Burn (a condition where the magic coursing through the body is more than the body can handle.) where they cease to exist in a gout of violet flame. These frantically scrawled scrolls would go on to become the basis for all formulaic magic in the future, and the sacrifice of the First Sages would become legend.
Once the Stellan temples' magical charge was consumed to safer levels and the Sages' Scrolls became archaic, many of the first Wizards began teaching in said temples. Equipped with dense books full of formulae that have been used, recorded, and improved upon; the Wizards were well prepared to begin writing instructions on magic- even full textbooks of magical theory and study. It was an enlightening period for the Arcane, and the wizards were the ones holding the torch. That is, until the repercussions of magic consumption came back from centuries before.
Wizards had spent hundreds of years learning and perfecting arcane magic across all cultures, learning of the nature of the worlds and learning what to expect from them. What they did not expect, however, was that The Sages left them more to ruminate on. Sorcerers were beginning to appear: people from all backgrounds which descend from any numerous people that were involved in the building of the Arcane, or even folk who got too close to a Stella Stone or another place of incredible Arcane Resonance.
So, to finally answer your question:
You can be born with magic, or even stumble into it! People of Gaia are definitely aware of magic, but there are places that outright fear it. You can learn magic formally from the Wizards of established schools, or from your parents/village smarties if magic is culturally relevant to your heritage. Humans of some cultures have restrictions on who can learn magic, and who has to learn magic to protect themselves; but like humans of our world, that philosophy on The Arcane is not etched in stone.
Money's involvement in magical education has less to do with your prowess and more to do with your style if you know what I mean. Formally taught wizards usually spend some coin to take their classes, and Hedge Mages of the same style can build a spellbook of their own design from a hodgepodge of acquired scrolls and research. While these legendary approaches can be pricey, or even scandalous in some human communities; there are avenues which cost nothing! You are still able to beseech power from The Gods, be granted magic as an Oracle to them, or even simply through understanding the way magic courses through the natural world as a Druid or an Alchemist.
When all is said and done, magic is simply a part of Gaia's past, present, and future. People from all walks find countless ways to access the mysterious essence of magic, and the obstacles that prevent folk from using it are few. Luckily for the mundane, arcane folk of genuine power are quite rare, as the aptitude for magic is highly reliant on keenness of mind and force of will. Many communities are yet agrarian, and place more value in a strong back than a strong mind.
I hope this wasn't too much! I felt like answering only one thing on this would have spawned many more questions (that I got answers to) so I thought maybe I could give a little background history.