Greek boats and ships
Because Greece was so mountainous, and every place in Greece was so close to the sea, a lot of people in Greece used boats to get from one place to another, even starting as early as the Stone Age, when people sailed to the islands to get obsidian, and also went out in boats to catch tuna fish.
Greek people used boats to fish, and to trade with other places, and also to sail to other cities and fight them and take their stuff. Greek sailors had different kinds of boats for all these things - small rowboats for fishing, and big trading ships, and fast warships. By the 600s BC, the Greeks were among the best sailors in the Mediterranean Sea (along with the Phoenicians).
Learn by doing: go out in a rowboat or sailboat
More about Greek warships
Ships and Seamanship in the Ancient World, by Lionel Casson (1971).
The Ancient Mariners, by Lionel Casson (2nd edition 1991).