When you are Level 20, go to Grand Master Tobias (Gludio) to become a Shilien Oracle. By l2hub
Steps from the game client
Two Books
Quest that must be fulfilled to change occupation to Shillien Oracle. Magister Sidra explains that to become a Shilien Oracle you must acquire two books written in ancient rune: the 'Garmiel book' and the 'Andariel book'. First you must visit Magister Talbot in the Village of Gludin, and learn how to obtain the Garmiel book.
Bloody Runes
Magister Talbot asks you to slay Dark Succubi and bring back five bloody runes. You will find those abominations in a spider nest west of the Altar of Rites. In return he will compile the Garmiel Book for you. Monsters to hunt: Dark Succubi.
You have obtained the Garmiel book from Magister Talbot. Now you must obtain the Andariel book from Priest Adonius at Einhasad Temple in Gludin Village.
Ritual of Atonement?
Priest Adonius promises you that if you slay the skeletons and zombies in the Ruins of Despair and bring back 10 Ashen Bones, he will give you a copy of the Andariel book. You should hunt Skeleton Infantrymen, Shield Skeletons, Zombie Soldiers and Zombie Warriors.