A train car is a large, reinforced platform that rests on two trucks. These are not trucks in the normal sense of the word, but are four wheeled frames with a suspension system and brakes. The trucks are attached to the platform by means of a ring of bearings, which allows the trucks to rotate when the train is going around turns. Trains, of course use tracks, which are cold rolled steel, and welded together. The wheels on the trucks have lips that prevent the car from slipping off the tracks.
There are many different types of train cars. They all have special uses and purposes. Many of them have their orgins in mining. This is from a United States centric perspective, and covers current, not historical technology. Cars are measured in length and carrying capacity. Most are 50-70 feet in length. Cars are made of high strength steel. Some parts are cast, others welded together from steel plates.
Automobile Racks: These come in two and three level versions. Two level versions are mainly used, given the prevalence of SUVs and light trucks. These trains are divided into short segments to be unloaded and loaded. Ramps are set up at the terminal end, and the car is driven up the ramp, through the first car, across a steel plate to the second car, and so on until it gets to the end. The reverse is true for unloading.
Box cars are 50-60 feet long and carry 70-100 tons. Box cars, such as the one Lenin was shipped back to Russia in are used for many things. They are used for goods which are more fragile. They come in reefer (thats refrigerator, not marijuana) and regular versions. Auto parts, appliances, and other goods that need protection from the weather are carried in box cars.
Flatbeds come in many shapes and sizes. There are standard flatbeds which have strap mounts on the sides for load control. Bulkhead cars have only front and rear walls, enabling better control for things like pipe. Centerbeam cars are used mainly for lumber. They have a beam and frame through the center, enabling things to be strapped tightly. Steel bars can be fitted vertically into slots on the side of flatbeds to carry lumber and pipes.
Intermodal Flatcars are cars that are used for moving different modes of transportation. To clarify, these are cars that carry truck trailers and standard 20 and 40 foot containers. Some are like flatbeds with extra mounts for standard 40 foot semi-truck trailers. Others are sunken to carry containers:
The car is sunken so that two containers can be nested on top of each other. This is important, as these cars have to be able to fit through tunnels.
Hopper cars are 50-70 feet long and carry 3000-6000 cubic feet of material. They are used for carrying bulk loose goods, like gravel and grain. They come in three models. Open top cars are used for carrying gravel and similar bulk goods. Covered hoppers are for goods that give off dust or goods that need protection from contamination like grain. Airslide cars are neat cars that have a thick fabric lining. To unload these, air is blown between the fabric and the metal of the car, forcing materials to move. These are used for sugar, grain, and flour.
Tankers carry 6500-32000 gallons. These carry liquids of all descriptions. They use that neat thing called gravity and load from the top, emptying from the bottom.
Passenger Cars come in many varieties as well. There are one and two level cars. Anyone who has seen an Amtrak train has seen it all. Many trains have two levels over the center section of the car, and one level over the wheels.
The information herein was gleaned from the uprr.com, the Union Pacific website, and my own knowledge. If I made an error or forgot something, please msg me.