Short answers, pulled from the story.
Divination functions as an attempt to gain insight into a question or situation via magic ritual or practice. It often contains a social character usually found within a religious context where diviners read signs, events, or omens through supernatural agencies such as spirits, gods, god-like-beings, or the will of the universe.
Oracles served as conduits for gods on earth where prophecies were understood as the will of gods verbatim while seers interpreted signs provided by gods rather than direct contact. Seers used many methods including extispicy and ornithomancy to explicate divine will and performed sacrifices at hiera and sphagia during battle to reveal appropriate omens before advancing.
Cicero attacked divination in De Divinatione during the 1st century BCE while Sextus Empiricus wrote Against the Astrologers in the 2nd century CE. Lucian devoted an essay to Alexander the false prophet between 125 and after 180 AD and modern scientific community dismisses it as superstitious because experiments do not support predictive reliability.
Astrology known as ilm ahkam al-nujum is most widespread divinatory science within Islam that studies how celestial entities apply to daily lives of people on earth. Science of sand or ilm al-raml translates as geomancy based on interpretation of figures traced on sand using deduction and computation to uncover significant prophecies unlike omens which read visible random events.
Divination was central component of ancient Mesoamerican religious life where Aztec gods described as diviners closely associated with sorcery and Tezcatlipoca served as patron of sorcerers and practitioners of magic. Visions derived from hallucinogens another important form still widely used among contemporary diviners of Mexico including morning glory jimson weed and peyote.