Short answers, pulled from the story.
Ancient Greek is the set of forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is divided into Mycenaean Greek around 1400, the Dark Ages around 1200, the Archaic or Homeric period around 800, and the Classical period around 500.
The main dialect groups of Ancient Greek were Attic and Ionic, Aeolic, Arcadocypriot, and Doric. Attic Greek became the basis of Koine Greek, while the Lesbian dialect, used in the surviving fragments of the poet Sappho, was Aeolic.
Ancient Greek had long and short vowels, many diphthongs, double and single consonants, voiced, voiceless, and aspirated stops, and a pitch accent. In Modern Greek all vowels and consonants are short, many vowels and diphthongs are pronounced as a single /i/ through iotacism, and the pitch accent has become a stress accent.
The earliest surviving examples of Ancient Greek writing, dated to around 1450 BC, are in the syllabic script Linear B. The Greek alphabet became standard beginning in the 8th century BC, with early texts written in boustrophedon style before left-to-right became standard during the classic period.
After the conquests of Alexander the Great in the late 4th century BC, a new international dialect called Koine, or Common Greek, developed, largely based on Attic Greek. By about the 6th century AD, Koine had slowly metamorphosed into Medieval Greek.
Ancient Greek is compulsory in all gymnasiums and lyceums in Greece, in the liceo classico in Italy, and in the gymnasium in the Netherlands, and is widely taught at universities as part of classics. In 2006/07, 15,000 pupils studied it in Germany and 280,000 studied it in Italy, and works including Harry Potter and the Philosopher's Stone have been translated into the language.