This is the most basic terminology in a single image:
A bit more verbose version is found in this slideshow, but there are a few factual errors, highlighted in the comments below.
The various parts are named based on their main characteristics, then their sizes in studs, as seen here:
After getting the hang of it, it's time to advance to ...
Great question. Others may have better answers for a more "realistic" design, but the math for a solid structure is actually pretty quick. Take the Empire State Building for example:
Base: 129m x 57m
Volume: 381m × 129m × 57m = 2 801 493m³
And a basic 2x4 brick:
Volume: 31.8mm × 15.8mm × 9.6mm = 4.823424e-6 m³
The number of bricks needed to ...
As far as I can find, there are very few official "scale" terms used in LEGO. The term "Minifig-scale" is a fan term and is fairly loose, as the scale of the figs themselves don't really equate to reasonable human dimensions. Add to that the fact that minifig-scale vehicles and buildings have had variable relative sizes compared to minifigs, making it ...
TLDR: Scale for train MOC is a personal preference based on the needs.
There is a lot of personal preferences here. Like, how do you decide if the LEGO track geometry should translate to standard gauge? Why not any other track gauge available in other countries? How do you scale the model if it originally use slightly wider gauge? So there'...
It looks like the best practice is to adjust the proportions to the constraints imposed by the media.
For example, the closest LEGO rendition of a modern high-speed train, the 10233 Horizon Express has cars that are built on a 6x28 chassis piece, which gives a very different width-length ratio than the ICE2 (3.02 m : 26.40 m). And it just works and looks ...
From the book Crazy Action Contraptions page 47 has a nice graphic showing the relation between the sizes of different pieces.
I'd add that it is more common to call a "sideways brick" a stud. All lego elements are measured in studs. Using the same example as on the far right of the image, this Technic Axle is four studs long.
Minifigs don't have the same proportions as average humans. They are comparable to a 600 pound male. Based on minifig height, the scale is about 1:45. Based on minifig width, the scale is about 1:32. If you're making a building, you probably want to follow a 1:45 scale. If you're making a vehicle, you probably want to go with a 1:32 scale. One rule of thumb ...