Each province produces one type of trade goods the goods produced is the largest determinant of the province's trade value. Trade steering is used for two primary purposes. In the recent years, the binary Eu4 Trade System options trading industry has observed a great impetus in its popularity. To move trade from areas where you have low power to areas where you are dominant, and to move trade from a node to the node where your capital is to avoid taking a trade power penalty. The problem is that I have only 3 merchants (2 base and +1 from Exploration/Expansion ideas). If it added 100 trade power, the marginal change for another 1 trade power would be. In this video I go over everything you need to know about the trading system in Europa Universalis 4, from the inception of trade value in provinces, to adva. Usually I don't care about that much because it need too much time to return me base investment, like, far more than one hundred year in severe case. No, really, for a game that can focus on exploration, knowing what the New World looked.
You control armies, manage religions and government systems, and can develop your own tenets and doctrines. Not cheap prices scale depending on the province and country development and opinion modifiers.