There are two ways to get started in Railpro:
1.) Buy the starter pack that comes with the power supply and the controller, as well as a couple of locomotive modules.
2.) Buy the power supply, a couple locomotive modules, and a CI-1. The CI-1 is a USB device that turns your computer into a controller. It is initially less expensive to go this route, but eventually you will probably want a controller, especially if you are running on other layouts.
Look around on Youtube for videos of Railpro. I have several on there, and there are some from others as well. That will at least give you an idea of the interface and capabilities.
-Kevin