Short answers, pulled from the story.
The Latin word sacrificium emerged from the combination of sacra meaning sacred things and facere which means to make or do. This term originally described priestly functions performed by individuals known as sacrificus.
Evidence of ritual animal killing appears at least since ancient Hebrews and Greeks existed. Ancient Egyptians forbade sacrificing animals other than sheep bulls calves male calves and geese within the cult of Apis.
E.B. Tylor proposed that sacrifices functioned as gifts to the divine valued either on their own merits or through the hardship they imposed. William Robertson Smith argued in The Religion of the Semites that the sole purpose was human communion with the divine through eating burnt offerings.
Corpses found at Knossos in Crete suggest Pre-Hellenic Minoan cultures practiced human sacrifice. The north house contained bones of children who appeared butchered while Phoenicians of Carthage left large numbers of children's skeletons buried with sacrificial animals.
Nicene Christianity teaches God became incarnate as Jesus to reconcile humanity separated by sin through original sin concepts. Christ replaced insufficient animal sacrifices of the Old Covenant as the Lamb of God.