The process of model railroad planning involves buying a model train set of a particular scale, then deciding on the scenery, the electronics that will accompany the model train set up, and the critical process of wiring the tracks. You may have very simple circuitry for a single locomotive and several rail cars.
There might also be a station which is very elementary that controls just one locomotive. Or you might have two or more locomotives running on the same track. This can require a feeder for each locomotive, receiving its power through bus wire from the power pack. There also might have more than one power pack in the layout.
Since the power pack is used to transform the AC current in your house into DC current for your train, it is one of the initial considerations when going about your model railroad planning. The power generated and sent to the locomotive is routed through the variable resistor which operates as a throttle. The new power packs are solid state devices and they have transistors to convert the AC current into DC current.
The space you have to make your model rail set up will determine the magnitude of model railroad planning required. You might have a modern tilting train moving in a very futuristic scenario of a busy modern city. You will have on the other side mountains, lakes, arches, and tunnels through which a steam engine is moving with some passengers in the coaches. The controls have to be monitored for example at the railway crossing the gate should go down when a train is passing by, the previous station should inform the next station that the train is about to reach, and the train must whistle when it is about to leave a station.
Wiring is an important issue in model railroad planning. Wrong wiring will lead to short circuits. Keep some extra wire on hand for when expand your model train set up in future and add more tracks. After the wiring has been done use a polarity tester to confirm that there are no short circuits. If you have a huge model train layout then it is best to use heavy gauge wire of 12 to 14 gauges as bus wiring. Use many feeders to make the circuit very safe and running for a long time.
You can solder wires to rail joiners and make the feeder connections. Soldering will give stronger wiring but expansion at a later stage will be difficult as these soldered bits have to be detached. Use of tape instead for contacts will make them easily detachable. Use wire nuts instead of tape. Better than tape is to emply soldering. After soldering remember to file away any soldering wire that juts out as otherwise the train wheels will face hindrances during movement.
Depending on your budget you would buy your model train set up. Spend much time in doing research. There are many model train hobby clubs and there is a huge material on the web for you to read. Join the model train club in your town and get help doing your model railroad planning.