Welcome to Trainz, and the world of route building.
I am going to suggest that you start with building a small route. Preferably a model railroad layout with some variety in terrain features. Lakes, ponds, streams, rivers, hills and scaled down mountains. Attempting to learn the terrain tools will be much easier at the MRR scale of things than the 1:1 scale of building a full route. You can learn the ins and outs by doing, and of course the tricks and tips by asking questions of us that have some surveyor experience, on this forum.
I unfortunately, like many others, got supremely ambitious back in the TS12 days, thinking I would build a fictional layout in the Grand Canyon... Which I did attempt, and got partially done. I even bought Transdem for importing DEM mapping data and had a good time learning that app, and ended up with fairly accurate terrain imported into Surveyor. The problem was that I chose a 26x13 kilometer chunk of the canyon area with what seemed (at the time) accessible sections of the Colorado river. After trying to build an interesting rail line that would zigzag it's way down to the river and back up again, and supremely UN-realistic bridges crossings, I gave up. It was too much work to achieve what I wanted, and it looked sillier the longer I kept at it. Finding desert cliff textures at that time was a real pain as well, everything available was too low res, or suffered from severe stretching issues on the semi-vertical cliff surfaces of the canyon map.
The old proverb of "Your eyes are bigger than your stomach" applies here, LOL. You can see what little full texturing work I actually got done in this FB album.
https://www.facebook.com/media/set/?set=a.1477970479566&type=3
The next attempt was a smaller fictional desert layout in Utah. It encompassed the Moab city area and the long, wide canyon west of the city, and the winding canyon that runs north. I gave up on that one after I realized the near impossibility of modeling the striated rock formations that dominate the area, and highly repetitive job of texturing the terrain over so much acreage. Tedious does not begin to describe the task. Just ask dangavel, who has been doing that just that for several years now on his Colorado routes.
I eventually got into building Model Railroads in Trainz and haven't looked back. I can build out an idea in a few months time, rather than many years, and then move onto the next idea. I finally released a couple of layouts last year, after having been futzing around since Trainz 2010 Engineers edition. But, I did get a great compliment from a forum Trainzer on my KleinStadt MRR layout, saying it was payware quality, and that N3V should look at it for how a good payware layout should be built (I take that one with a grain of salt, LOL) and another on my Sissiboo NG layout, saying it was one of the funnest NG layouts he's run on.
I currently have around a dozen MRR layouts in the works, with a modified Rio Grande Southern layout, (from the March 2011 issue of Model Railroader) releasing next week, and the Sissiboo Lumber & Railway - Extended which takes half the original Sissiboo layout and adds it to a Rob Chant trackplan and a mining extension that I designed to make a nice multi-ops period layout. All of these include many of my own scenery models that i have built over the last year. Something like 150-ish new models, and a bunch of reskins and re-meshes of older Trainz assets.
So, take it slow, build small, build what you know and you will learn and progress at your own pace and be happier over the long run, than if you get overly ambitious and decide to build 400 miles of double track mainline and all the industries, cities and towns it encompasses.
Rico
and yea im very much an apprentice/rookie. ive dabbled with route building very minorly in train sim classic, but i only just got trainz yesturday and wanted to give it a go haha