Short answers, pulled from the story.
Maat refers to the fundamental order of the universe established at creation. This concept distinguishes the world from the chaotic primordial ocean that preceded it and encompasses both proper human behavior and normal functioning of natural forces.
The Pyramid Texts date to the 24th century BC and represent the first major source of Egyptian mythology. These inscriptions inside pyramids contained several hundred incantations intended to help kings pass safely into the afterlife.
Osiris is killed and his position usurped by his brother Set, with some versions describing him being dismembered and his corpse pieces scattered across Egypt. His sister and wife Isis finds her husband's body and restores it to wholeness before briefly reviving him to conceive an heir named Horus.
The Nile River flooded each year renewing the soil and allowing farming that sustained ancient Egyptian civilization while the sun rose and set daily bringing life to the land. This cycle of water and light shaped how people viewed time as a series of recurring patterns rather than a straight line.
At night Ra passes beyond the western horizon into Duat where he meets Osiris and merges into a single being reflecting continuous repeating pattern vision. Once united with Osiris' regenerative power Ra continues his journey with renewed vitality enabling dawn emergence seen as rebirth expressed by metaphor where Nut gives birth to Ra after swallowing him.