Trains no longer use cabooses. The crew stayed in a place in a town where the train stopped. All the cars in the middle are for carrying cargo - a load of things that people want moved. The locomotive is usually at the front of the train - the first car on the train. The locomotive is the part of the train that produces the power to make the train move.
Modern locomotives use electricity and diesel fuel for power.
Older locomotives used steam for power and were called steam locomotives. Steam makes the steam locomotive move. Steam comes from water. It looks like smoke but it is not. It is steam.