Waterways are what ships travel on. There are 3 kinds of waterways:
The first is plain sea. This is a very easy way to get transportation as there's usually an abundance of water on every map. So the only things you need to build are docks a shipyard and the ship itself.
The second type is rivers. There are some rivers which cannot be navigated as they are too narrow. But as they get larger boats can travel faster along them.
The third type is a canal. A canal can be used to connect a patch of sea to a city not near the sea or two cities not near the sea at all. There are canal bridges which can be used to cross with other waytypes.
The first is plain sea. This is a very easy way to get transportation as there's usually an abundance of water on every map. So the only things you need to build are docks a shipyard and the ship itself.
The second type is rivers. There are some rivers which cannot be navigated as they are too narrow. But as they get larger boats can travel faster along them.
The third type is a canal. A canal can be used to connect a patch of sea to a city not near the sea or two cities not near the sea at all. There are canal bridges which can be used to cross with other waytypes.