Traveling for the Greeks was very hard because land had many rocks that would break the wooden wheels that are used to carry people. Instead, they use water to travel from one place to another.
Back then they didn't have enough space for growing crops. So they expand the land space so that they can grow even more crops. And their weren't any main rivers to give water to the crops so that it can grow.
Greek traders needed some kind of transportation to get from one town to another for trading. So they used the ships to sail. Going on water was so easy even though you are just transorting from one Greek town to another because Greek was so mountanious.
The poppulation of Greece grew quickly. the amount of food that Greece could not feed all the people. So they startd a colony. Those colonies would send peopple over seas to see any kind of island tat they can settle at and start their colony there. Before they would do these kinds of stuff, they would always ask for consultation from an oracle.