For some of the things I'm doing lately, I've had to learn AutoCAD. Did I choose a simple "box" building for my "initiation" ???? Hoo Hah! not me! No I decide to do a 38' boat for my first project. Crazy?, yes, like a fox. The project steepened the learning curve, and threw everything at me at once! What a ride!!! I am learning what can, and cannot be done, with this tool, far more quickly than I would have if I'd been "cautious".
OK, I'll get to the point. I know how to design a boat, at least well enough to make a model of it. The challenge, then, was to learn how to use the software to do what I've done with pencil and ruler, and the basic knowlege of boat design. Designing a layout with planning software, is a double edged sword. You have to learn how to use the software, at the same time you are learning to plan a layout. It's possible, and can be a fun trip, if you like being on the sharp rise of the learning curve. It would be easier, to first learn the skill, and then learn a new tool to perform the skill with. Yes, layout design software is a tool, nothing more. Layout planning is a skill. The two go hand in hand, but still must be learned, each in its own way. The software can only show you where the track will fit, in a given space. You must provide the list of industries, the vision of the terrain, the era of operation, and the prototype railroad (if you are modeling a prototype). In short, You must provide the idea, the software will allow you to put the idea on "paper", and help you fit it into the available space.
The "Givens and Druthers" form at the top of this forum will help develope the idea.