The School of Evocation focuses on dealing damage through powerful spells. This is the school of barely contained magical power, roiling and raging against confinement and control.
Evokers focus their study on magic that creates powerful effects such as bitter cold, searing flame, rolling thunder, crackling lightning, and burning acid. Some evokers find employment in military forces, serving as artillery to blast enemy armies from afar. Others use their spectacular power to protect the weak, while some seek their own gain as bandits, adventurers, or aspiring tyrants.
History
Evocation was the first magic to be discovered, or, arguably, created. It emerged easily from the fabric of The Astral Plane, and its discovery paved the way for the formalization of subsequent forms of magic, the laws of Evocation serving as a baseline from which further laws of magic were derived.
While all magic uses The Astral Plane to power spells, Evocation magic deals directly with The Astral Plane, shaping spell effects entirely from raw magic, making it both exceptionally powerful and exceptionally volatile. Many find it the easiest school to learn, but the hardest to control, and many give Evoker novices a wide berth for fear of accidentally being incinerated in a spell gone wild.
Scholars believe that the effects of many Evocation spells could be accomplished by other means, such as Conjuring a blazing ball of fire from the Plane of Fire to achieve a Fireball (and thus allowing other elemental types to easily be conjured in place of fire), but there is little incentive to pursue this innovation outside of academic curiosity. Some go so far as to argue that Evocation is not actually a proper school, and that all Evocation spells are in fact flawed or incomplete forms of spells which truly belong to one of the other 7 schools. This of course brings into question whether or not the schools of magic are real categories laid out by the universe, or arbitrary inventions of utility and constraint.

Evocation is the purest school of magic, interacting most closely with The Astral Plane. While Conjuration might pull creatures and environmental affects from across planes, and Transmutation reshapes what is already present, Evocation spells consist of powerful magical energy shaped directly from the Weave itself, raw magic turned into blazing fire or lightning or radiance or light.