Alastor Crowley stated that "magick is the art and science of creating change in accordance with will."
First we look at art and science. Art being a concept of visualization! Creativeness. Stepping outside the norms of thought and daring to do something beyond us or challenging that which we believe above us wether it be God/Godess or even fear. Science is the realm of knowledge. The scientific method. Theories put to the test or laid to rest! Science also being our scope of reality! That which we know is factual, that which we know is possible, and that which we know is impossible.
One of the definitions of create is "to evolve from one's own thought or imagination, as a work of art or an invention."
So we are creating or evolving from our mind change. Change on not just a physical level but also a spiritual level. So through art and science we are creating change in accordance with our will.
However we don't always get what we want! If we did entire economies would collapse. Sometimes we don't consider the consequences of what we want or ask for. Sometimes we just want the impossible and need to become comfortable being just who we are! And then there are times we get what we want just not in the form we thought it would come.