Magic is broken up into many schools, each with their own spells. You will be good at it when you practice casting spell a lot. Higher skilled spells will evolve and start to travel faster through the air. They can do more damage, or even shoot multiple projectiles.
Since there are many schools magic is broken up into, each skill has different level power. In general, higher level spell is more powerful than that at low level. Players have to focus on making decisions about which school to pursue. New spells and schools of magic close their door as you are going further on the road to prerequisite school, and some restrictions begin to be seen down the road. You are not allowed to be an expect on schools of magic that are polar opposite, such as Fire and Water, Earth and Air.