By reading some specific titles, the creature that Frankenstein created learns all he needs to learn about humanity, including the fact that he has no place in it. This eventually generates an agony in him, as well as hate for his creator.
While the creature observes Felix and his family in the cottage, he discovers some of humanity's great gifts: music, for instance, as well as familial love and, of course, language. As Felix, one of the cottagers, instructs Safie, the creature also learns through these lessons. The book Felix reads aloud to Safie (and, unwittingly, to the creature) is Ruins of Empires, by Volney:
Through this work I obtained a cursory knowledge of history and a view of the several empires at present existing in the world; it gave me an insight into the manners, governments, and religions of the different nations of the earth. (chapter 13)
The creature wonders at the marvels of human history, but at the same time, he discovers vice and evil:
For a long time I could not conceive how one man could go forth to murder his fellow, or even why there were laws and governments; but when I heard details of vice and bloodshed, my wonder ceased and I turned away with disgust and loathing. (chapter 13)
He also learns the value of the property, the facts of life, and the concept of family, and he can finally tell he is not a human being but a "monster." This makes him miserable.
Later, in chapter 15, he finds in the woods a leather portmanteau containing three more books: Milton's Paradise Lost, a volume of Plutarch's Lives, and the Sorrows of Werter by Goethe, and he treasures them. By reading these volumes, the creature learns more about human nature:
They produced in me an infinity of new images and feelings, that sometimes raised me to ecstasy, but more frequently sunk me into the lowest dejection. (chapter 14)
By reading Werter, the creature begins to ask himself about his true nature.
Plutarch teaches him about virtue and vice and provides him a wider knowledge of human society:
The cottage of my protectors had been the only school in which I had studied human nature, but this book developed new and mightier scenes of action. (chapter 14)
Finally, Paradise Lost creates in him the need to search for God: his god, his creator. He relates himself both to Adam (since he has no father or mother) and to Satan, as he begins to envy the bliss of his protectors.
All these readings prepare the creature to confront the truth about his origins. Indeed, after becoming a competent reader, he can read Frankenstein's journal accounting his own creation. This awakens feelings of self-loathing, which will eventually guide the creature toward revenge and turn him into a real monster.