Magic, as practiced by humans, is not as simple as reading a spellbook.
Within this universe, magical aptitude is something people are born with. Though it is widely beleived to be genetic, occasionally things turn about to prove otherwise, but those with magic users in the family frequently wind up with more as you go down the line.
Magic users are attuned to particular kinds of magic. As far as humans are aware, these seem to be based around the five classical elements, fire, water, air, earth and void. In a sense, a person is born attuned not just to that particular element, but to a number of concepts to which one would attribute to that element. For example, air adepts are fast, deceptive and good at getting into places, they are also unnaturely good at escaping from situations! Fire adepts are, well, feiry! Water adepts are masterful traders and capable of understanding people's perspectives, earth adepts are just plain stubborn and void adepts are just that, void.
There are several roads of study for those interested in magic. The most obvious is joining a monastic order which focuses on magic, there are several in Europe and this is where most adepts, with no small amount of nudging from the church, will end up. Teutonic orders also accept adepts, though they will be subject to a more harsh learning curve. Some adepts avoid the attentions of the church and either attempt to practice magic on their own or refuse to acknowledge their capability.
Magical skill is broken down by the abbots who beat it into their underlings as consisting of five teirs. The first teir allows an adept a slightly closer relationship with his element. He might be able to sense its presence or affect it in some small, largely unnoticable way. They also more than likely affect those around them, as well as themselves, with the ethos of their element. Fire adepts are constantly starting fights, (and fires!) water adepts encourage discussion etc.
The second teir allows a stronger control on their element, fire adepts can make fires burn hotter, as well as being able to know how to wreak as much damage as possible in many situations, social or otherwise.
Third tier adepts effect noticable control on the world around them. Water adepts can cause the clouds to rain, rivers to run faster as well as knowing exactly what to say in a given situation. They cannot yet levy truley powerful force from nowhere, but any witnesses of their work will question it's coincidence.
Fourth tier usually implies that the adept can now bring forth his element from nothing. The feat is known as autogeneration and is a well acknowledged bench mark of power. Some adepts can effect this earlier than fourth tier, but this level skill is when they are actually perceived to be to control it.
Fifith tier is a rare and terrifying level of skill, the adept is now truly of a wizard of terrifying power. Generally those of this level can demosntrate consumption; converting themselves into their chosen element and controlling that element anywhere within range. There are only a handful of such individuals in Europe, indeed, the whole world.
