The goal of the game is to make money either by trading or by sinking and plunder other players ships. Until you have built up to a more powerful ship, it is best to stick with trading.

You sail from one port to another buying and selling goods. Generally the best good to buy is the one locally produced, which is the first on the list. You will never fail with this tactic, but over time you will find some other goods are even better based upon economic conditions.

Once you earn enough gold, you can buy bigger and better ships, and possibly arm them to the teeth to plunder treasure from other players ships.

Read this article on how to play for more info