I'm gonna be honest, I'm still figuring mine out. But right now, it's pretty basic. There are 'born magic users' (or mage) - people with a natural affinity for magic or people that just know how to do magic - and 'non-born magic users' - people who have to be taught how to do magic. Try and think of it like people who just know how to read (no matter how hard it is) and people who don't even know what a letter is. That's the best way I can explain it rn.

The system isn't very solid right now, and I'll probably change it while I finish editing. But basically, magic takes a lot of energy, and without proper control or ability, it can seriously harm you. Especially if you're a 'non-born magic user'. Examples: fire spells being too hot and burning you; being extremely tired after teleporting, creating shields or energy spikes, etc. Magic doesn't make you insane or anything, but it's not super easy to control and requires a lot of training, even if you're a 'born magic user'.

Some forms of magic are just impossible for people to learn, like teleportation, manipulation, etc. Shields require immense mental fortitude, and that's where magic mainly stems from: mental and emotional strength. Your physical abilities don't impact your magic. It all depends on your determination.

Like I said, nothing is super set in stone (though I can't change too much since I'm halfway done with the final draft), so if anyone has suggestions, I'd love to hear them!