For vibration testing, we can simplify a machine to one or two shafts with two bearings each and something connecting the shafts. Look at your machine and identify the shaft(s), bearings, coupling, and driven component. 

A machine train is made up of a prime mover, a power transfer unit, and a driven component.  Some complex machines are really just two or more standard machines combined.  Select the machine type like your machine is constructed in real life.