Answer:
The musical begins with Galinda and we see where she is at in present day. While they are talking about the Wicked Witch of The West (Elphaba), one of the Ozians (People of Oz) asks Galinda if it is true she knew Elphaba. Galinda is hesitant to say that they were friends, so instead she tells them that they did go to school together and the story of how the Wicked Witch came to be begins. Focusing on her early days before she was conceived, Elphaba's thought to be Father (Governor of Munchkin Land) had gone away and left Elphaba's mother alone. Elphaba's mother has an affair with an unknown man at the time and they drink a green elixr. Most believe this is the cause of her green skin. When her husband returns Elphabas's mother is pregnant with a child, but the Governor assumes it is his and she does not tell him otherwise. Elphaba is born with green skin and the father basically rejects her. When the mother is pregnant again the father makes her eat milkflower, so the baby will not come out green like Elphaba. This milkflower causes the child to be born handicap. The mother dies while giving birth to Nessarose. The Governor is the biological father of Nessarose, whom he obviously adores more over Elphaba. He sends them to Shi z University where Elphaba ends up rooming with Galinda, whose perky personality earns her a popular image. The headmistress lets Nessa room with her and Elphaba becomes angry and is overwhelm with this power. This power that the headmistress experiences causes her to teach her special magic classes that have not be taught in years. This is a class that Galinda has wanted to be in, but was not allowed to. A student who had been kicked out of schools is named Fiyero and Galinda right away is in love with him. They go to a dance and Boq(a munchkin who adores Galinda) goes with Nessa at Galindas nudging. Galinda gifts Elphaba a hat, but Elphaba takes it as sincere and gifts Galinda back with a spot in her magic class. Later Elphaba dances awkwardly and Galinda joins her, bonding over this and becoming friends.
The entire musical is based on the quote, "Are people born wicked, or is it wickedness thrust upon them?". This musical tells the story of Elphaba, better known as The Wicked Witch of The West, before she met Dorothy and how her close relationships shaped her reputation. After doing good over and over Elphaba is given this idea that every good deed she attempts never goes unpunished. There are major consequences for her gifts, but she had always intended good.