HOBBY BASICS

Well, the hobby is all about this love for trains. However, there are many facets to this hobby which makes the tribe of railway hobbyists a motley blend with varied interests – all stemming from the love of trains. So while one could be quite content being a collector of a specific epoch, or a railroad route, another could be lucky to get space to model his collections on a working layout. The "layout" refers to the replica of (or semblance to) a railroad and the landscape it passes through. This includes the rail side buildings, countryside, water bodies, bridges, stations, platforms and depots. All this makes kit building a natural extension to a modeler’s love for trains. What also has to belong to the skill set of a hobbyists is elementary understanding of electricals and wiring because in this surreal world of modeling the signals have to work, tracks have to change, trains have to start and stop without human intervention, and the buildings have to be lit up. 
Commercially, miniature trains are available in different scales. Modelers pick their scale depending upon what fascinates them and according to the space at their disposal.
H0 scale is the most popular. In this scale (half of O scale), 3.5 mm (0.14 in) represents 1 real foot; this ratio works out to about 1:87.086. In H0, rails are usually spaced 16.5 mm (0.650 in). HO scale has a large presence in the market place with thousands of accessories available in this miniature size. One can collect trains, tracks, frogs (points), buildings, signals, catenaries, human figures – all reduced to scale and go on to build an imaginary or a prototypical layout. HO’s size allows modelers to fit more details and more scale miles into an area. Those who want more of this, model in N scale (1:160). Smaller still is Z scale (1:220).
Garden trains are synonymous to LGB. The G scale as it is known, is available in the ratios 1:20.3/1:32 and runs on a 45mm gauge track. These trains are great for outdoors, and when  middle age, myopia sets in. However, owing to their size, they are demanding on space. Made to withstand the vagaries of nature, these trains can be used simply to beautify and liven up a garden, or made to run through open air layouts.

Scale Reference

Z (1:220)
N (1:160)
HO/OO (1:87/1: 76)
S (1:64)
O (1:48)
G (1:20.3; 1:32)

Conventionally, model trains (except for Marklin) run on two-rail track, which is powered by a  DC power supply. Voltage supply to the tracks is varied to alter speed and polarity changed to reverse direction of travel. With the advent of DCC (Digital Command Control) trains now correspond with the power controller through decoders installed in them and provide use of “functions” to control sound and light. DCC of course has become mandatory for enthusiasts who indulge in prototypical operations of a railroad.

Truly, rail modeling can only be constrained due to reasons of space, funds or imagination