As with Passenger Liners, Freight Haulers can be either System Ships or Star Ships working regular routes within the same system or routes between various star systems.  They can also be independent haulers or operate under the charter of a larger corporation.

Freight Hauling is a bit more complicated than passenger liners, as the prices of various cargo's varies between the sources and the many destinations, as outlined in the Freight Hauling thread:  link to a message in this game

Use the Game Wiki The Frontier page to determine where you want to pick up your cargo.  Once you know what your cargo is, then you can decide on the most lucrative destination.