Why didmany people in ancient greece make their living from the se?

Most people in Ancient Greece made their living from the sea because Greece was an area surrounded by seas, and its mainland territories weren't suitable for agriculture. So, whereas other ancient civilizations mainly lived from agriculture, Greece thrived on trade, as the soil wasn't good enough for crops. There were Greek city-states not only in the southern tip of the Balkan peninsula (where Greece is today), but also throughout the Mediterranean basin, all the way to Italian peninsula to the west and Asia Minor to the east. So, this trade network was very developed, and the majority of the trade was done by ships. Of course, just like many other ancient civilizations, the Greeks were also great warriors, which was another valuable source of income.

The answer is installation.