How you build themEdit
Freight cars are built in the Railyard, one of the buildings in the top right quarter of your capital as displayed on the "Give Industry Orders" screen. Each one costs one unit of steel and one of lumber and needs two labor units during the turn-end in which it is created.
What they doEdit
They appear and can be filled, one unit per car, on the "Give Transport Orders" screen.
In a standard game you can expect to see fifteen of them initially, more than enough to carry everything you are producing and enough to carry your initial three army units.
As you build ports and depots, and/or raise tile productivity to higher levels, and/or start to get materials from villages and later goods from towns, more cars will be needed if you are to avoid waste.
The subsidiary value of your transport system, in addition to its regular job of carrying items to your capital, is the rapid movement of Army units to non-adjacent provinces of your empire (even overseas). An attempt to move them will show a black railroad engine icon in any available target province. However, the icon is misleading, because the capacity for that movement is based on your number of freight cars, not on the length or location of railroad: five cars are needed for every "gun" that went into the assembly of each regiment involved.