Short answers, pulled from the story.
Ancient Greek religion had no revealed scriptures. Works such as Homer's Iliad and Odyssey, Hesiod's Theogony and Works and Days, and Pindar's Odes were regarded as authoritative and perhaps inspired, but not as canonical scripture binding on all worshipers. Orphic and mystery cults maintained their own texts, but these were respected only within those circles.
Most ancient Greeks recognized Zeus, Hera, Poseidon, Demeter, Athena, Ares, Aphrodite, Apollo, Artemis, Hephaestus, and Hermes as eleven of the twelve, with either Hestia or Dionysus occupying the twelfth position. Each deity governed specific domains, such as Zeus over the sky, Poseidon over the sea and earthquakes, and Aphrodite over love.
Animal sacrifice was the central act of worship in ancient Greek religion, conducted at outdoor altars with hymns and prayers. Sheep were the most common sacrificial animal, followed by cattle, goats, pigs, and poultry. The inedible portions were burnt as the deity's share while participants ate the meat, a practice Homer's Odyssey and Iliad describe in detail.
Official persecution began under Emperor Theodosius I in 381 CE, who disbanded priesthoods, destroyed temples, and prohibited worship of pagan gods in public and private homes. The last Olympic Games were held in 393 CE. Isolated communities, such as the Maniots of the Mani Peninsula in Greece, maintained the old religion until at least the 9th century.
Mystery religions were cults that required initiation before their secrets were revealed. They offered what public religion did not: mystical experience, systematic doctrine, a map to the afterlife, and communal fellowship. The mysteries of Eleusis and Samothrace were among the oldest and most local; the mysteries of Dionysus spread more widely across the Greek world.
When Rome conquered Greece in 146 BCE, it absorbed much of Greek religion into its own. Greek gods were directly equated with Roman counterparts: Zeus with Jupiter, Hera with Juno, Poseidon with Neptune, Aphrodite with Venus, Ares with Mars, Athena with Minerva, and Hermes with Mercury. Some gods, including Apollo and Bacchus, had been adopted by the Romans even earlier.