Hi Phil
As has already been said, you use surveyor. This is a much simpler to use route/layout building system to MSTS

And will allow you to build much further much quicker, as a beginner
If you want DEM made routes, your best bet is either use the above mentioned programs, or ask around to see if anyone has done a DEM for the area you want.
Oh yes, and you might find content creation a bit difficult, we use GMax and not TSM

Then again, we have a wonderful community here that will be more than willing to give you a hand with creating things, so long as your prepared to listen
Welcome to the life taker, Trainz

Say goodbye to all loved ones, and hello to Trainz...
Zec