On the most basic level 3D Railroad is a specialized CAD program, that draws track. In the picture below is a classic twice around 4'x8' layout. Here I have used a combination of sectional track and flex track. Sectional track can be manually defined, but it is much easier to use predefined sectional track from a library database. In this case, I have used Atlas HO track.
Libraries provide track, structures, scenery, rolling stock, etc.
The libraries are a mixed blessing. On the positive side, Abracadata has provided additional libraries on their web site. The interface is intuitive to users that are familiar with drafting and CAD programs such as Adobe Illustrator, Macromedia Freehand or Vector Works. 3D Railroad offers a number of free floating palettes. Flex track is drawn as a bezier and can be manipulated in the usual manner.