The Hellenistic period begins in 323 BC, with the death of Alexander the Great, and ends in 146 BC with the Roman conquest of Greece.
Questions about the Hellenistic period should be about historical events in the wider Greek speaking world during the era. Strictly speaking questions about Alexander the Great belong to the immediately prior period of Greek history, Classical Greece, but Alexander is more relevant to the Hellenistic than the Classical period.
The Wikipedia article on the period is fairly thorough, please read it before you ask a question about the era.
- Did Alexander the Great destroy a city to demonstrate his ability to reign?
- How did Alexander III of Macedon get the title "the Great"?
ancient-greece for general questions about ancient Greece,
greek-dark-ages for questions specific to the Greek Dark Ages (the Homeric era),
classical-greece for questions specific to the Classical period,
greco-persian-wars for questions specific to the Greco-Persian Wars,
hellenistic-greece for questions about the Hellenistic period,
alexander-iii-greece for questions specific to Alexander the Great,
macedon for questions about the ancient kingdom of Macedon,
greek-mythology for questions about the myths of Ancient Greece (but please read this relevant Meta discussion before asking mythological questions).