Magic is the ability to manage the principles of the universe by means of an energy called mana.
Mana is the unique energy possessed by every living being. It is created in the body of every life form in a different way and form that facilitates or hinders its use.
Magic is a tool that anyone can learn as long as they possess the aptitudes, the potential to use it and a mental image of the phenomenon to handle.
Aptitude is measured with the color scale of the visible light spectrum, red being the total absence of mana suitable for use while violet represents being blessed by mana and always being able to use it in the most efficient way as long as you have a clear mental image. Aptitude is something you are born with and is unbeatable.
Potential is measured in numbers from 0 to 9, which determine the strength and scale of the magics at your disposal. Unlike aptitude, potential improves as you train and gain experience. The speed at which you obtain higher numbers depends directly on your aptitude, with violets being those with monstrous growth speeds; greens those who grow at a normal rate; and oranges who go at the slowest rate (reds do not grow from zero potential).
Mental imagery is the process by which you create the mental postulates that will allow you to perform magic. "You can't mine gold without knowing what gold is and its properties."
One more fact to know is that all spells from level 1 to 6 are tabulated in magic books, with their respective mental image. The only spells that are not available to the general public are those that are tied to unique abilities or lineage, aside from spells level 7 and up.