Excerpt from [wikipedia]:
“In the chronology of the series, Skyward Sword is a prequel to Ocarina of Time, and elaborates on the origins of the Master Sword andGanon. According to legend, after the creation of Hyrule, the Triforce was entrusted by the Golden Goddesses Din, Farore and Nayru to the deity known as Hylia. However, the Demon King Demise gathered an army to take the Triforce for his own evil intent. Using her power to create the floating islands called Skyloft to keep the Hylians and the Triforce safe, Hylia and the remaining tribes—the Ancient Robots, the Parella, the Kikwis, the Gorons, and the Mogmas—battled Demise’s horde before the demon was defeated.
The plot begins many years after the prologue and follows an incarnation of the protagonist Link, who was born and raised in Skyloft, who begins to have dreams of a strange figure. Woken up by his childhood friend Zelda, Link gets ready for the Wing Ceremony, a tradition to acknowledge one as knight. Link completes the ceremony after overcoming the attempts of a classmate, Groose (バドBado), to sabotage him. However, Zelda is then taken in by a storm which sucks her down to the still demon-infested Hyrule. Soon after, Link learns that the figure from his dream is Fi (ファイ Fai), the spirit of the Goddess Sword which Hylia created in case the evil she defeated was to stir again. With guidance from an elderly woman in the Sealed Shrine, Link pursues Zelda to the Skyview Spring where he encounters the Demon Lord Ghirahim, who is responsible for Zelda’s predicament. However, tracking her down to the Earth Spring, Link learns that Zelda is being protected by a mysterious woman named Impa. It is later at the Lanayru Mining Facility that Link receives the Goddess Harp from Zelda, as she and Impa depart into the past through a Gate of Time before it is destroyed during the fight with Ghirahim. Later, when Groose ends up following Link to the surface before fighting the monster known as the “The Imprisoned”, the elderly woman advises Link to seek out three sacred flames of the Golden Goddesses in order to increase the power of his sword to activate the second Gate of Time within the temple. Along the way, he also strengthens his spirit through the trials set by the three Goddesses. Once all three flames are infused into it, the Goddess Sword transforms into the Master Sword and he is able to enter the Gate of Time, arriving in the time period where Demise was just recently sealed away by the Goddess.”