When you have been told to do so by your teacher at the right time, you venture through the ring of trees and into the spotless clearing, and there you pray. Then, depending on your element, your creature will come to you, either from the ground, from the sky, from a flame that will erupt before you, or from a spring that will flow in front of you.

The people in this world believe that when you die, your creature goes back to protect the forest until you are reincarnated, at which point it reverts to the element from whence it came until you are ready to summon it again in a new form. So for fear of the creatures of the dead, people do not enter the forest until it is their time.