While most humans are touched by the magic that flows thru the world (like water) and can use some abilities, a rare few have the ability to actually sense and shape that magic. Those few are called Mages (surprise!), and they need years of training to adequately take pieces of the flow and shape it into what they desire.
Controlling the magic mainly takes concentration. Some hand gestures, circles, and words help the shaping along for most spells. Big works require circles and some material components, and depending on how big, more mages. Spells aren’t set in stone; a mage with a good imagination and concentration can make the magic do just about anything he/she wants.
There is at least one school that will teach any child with the ‘Mage Talent.’ This school was started shortly after The Rift by a regular human (who knew quite a bit about Mages and Magic) named Jack Oberon. However, by when he made that school, the ‘Mage Talent’ seemed much more prolific than it is now. This school teaches Mages for free (because an untrained Mage can become a problem), but it also offers classes for regular humans (for a price).
There’s a full-ride scholarship for regular humans called the “Mage Hunter Scholarship.” This scholarship is supremely hard to get (just about the only ones in the past who were able to get it were the First Anima), and anyone who gets it takes a lot of classes with the Mages to better learn how to mundanely defend themselves from magic. As the title of the scholarship implies, these humans take the training to be able to hunt down renegade Mages and other evil stuff. You might be thinking “WTF?! How is that possible?” Well, regular, completely mundane humans (with no magical talents whatsoever) who spend time around Mages somehow gain an immunity to certain forms of magic: mind reading and all forms of scrying, mainly. This is an anomaly that people have been trying to research since it pretty much was discovered, and it still stumps them.