How does magic work?

So, you wish to master the arcane arts.

The land of Ávra is steeped in Aura, the source of all arcane. Everyone interacts with the Aura in one way or another, even if they don't realize it; those who choose to harness the magnificent massive magics willfully have a powerful and diverse array of abilities availed to them. Your characters ability to wield magic is closely tied to their career, as such, the use of magic is performed in much the same way as any other action within the game. But, like actions involving your career, Magical actions can be as natural as breathing or severely difficult to perform based on your character's lore and inherent magical ability.
All magical characters start the game with no set magical skills, and must attempt to use a magical skill in order to gain it permanently. As with all action in the game, the DM will require you to roll a challenge roll when performing a magical ability, what die and the winning condition taking your magical abilities as laid out in your lore, into account. If a wandering knight were to attempt to utilize Fireball, he may have to roll 4 d20's and all four must land on natural 20's to perform the skill, as his lore dictates that he is not inherently magically attuned or have any magical training. On the other hand, a learned and wisened wizard character would only need to roll a d10 and get 5 or higher to perform the spell. 
No matter what, if you achieve the winning condition, congratulations, you've performed the spell! In order to permantely learn the spell and no longer need to roll challenge rolls for it, you MUST roll a natural high, just like any other skill. Once you do, you have the option to learn that spell permamently, and it will become one of your skills moving forward.
Some magical abilities will also have daily limits, or timed uses. A good example of this is the Fae's natural ability, "Pixie Sticks", which can only be performed once a day. These limits exist to ensure that Aura users are not overwhelming themselves or the game.