Short answers, pulled from the story.
Horus was the Egyptian war and sky deity who embodied the physical space of the heavens. He was the first known national god of Egypt and the patron of Lower Egypt. The Egyptians believed the sun was his right eye and the moon was his left eye.
The worship of Horus began in the late prehistoric period before the first stone pyramid was laid. This belief persisted from the early days of Egyptian history until the Roman occupation. The people of Nekhen named the falcon Horus as their first known national god.
Horus fought Set to reclaim the throne stolen by the usurper who murdered his father Osiris. The conflict represented the struggle between Horus, the patron of Lower Egypt, and Set, the patron of Upper Egypt. The myth justified the political reality of a unified Egypt under the rule of the pharaoh.
Set gouged out Horus's left eye during the struggle, which became the Wedjat or Eye of Horus. This symbol of protection and royal power was painted on the bows of ships to ensure safe travel. The loss of the eye explained why the moon was dimmer than the sun.
The pharaoh was identified directly with Horus in life and became Osiris in death. The king's name was often written with the falcon hieroglyph, and the royal titulary included the titles of Horus. This theological framework gave the ruler absolute authority over the land.
The annual Festival of Victory known as Heb Nekhtet was held at the Temple of Horus at Edfu during the second month of the Season of the Emergence. The ritual featured the king or a priest playing the role of Horus striking a hippopotamus representing Set with a harpoon. This sacred drama reenacted the battle to legitimize the king's rule and preserve cosmic order.