This table gives the Greek letters, their names, equivalent English letters, and tips for pronouncing those letters which are pronounced differently from the equivalent English letters. (There are actually several acceptable ways to pronounce New Testament Greek. For the gory details, look here.)
The Greek alphabet emerged several centuries after the fall of Mycenaean civilization and consequent extinction of its Linear B script, an early Greek writing system. Linear B is descended from Linear A, which was developed by the Minoans, whose language was probably unrelated to Greek; consequently the Minoan syllabary did not provide an ideal medium for the transliteration of Greek language sounds. The Greek alphabet we recognize today arose after the illiterate Greek Dark Ages — the period between the downfall of Mycenae (ca. 1200 BC) and the rise of Ancient Greece, which begins with the appearance of the epics of Homer, around 800 BC, and the institution of the Ancient Olympic Games in 776 BC.