Instructions
Choose an inexpensive but reliable starter set. (HO's popularity pays off in manufacturing volumes that permit this "middle-of-the-road" size to offer generally lower prices than those found in scales larger and smaller.) You want something with a small diesel engine and a few cars, some sectional track---enough to create a loop---and a power pack, which will convert your home's alternating current (AC) to the direct current (DC) used to run your trains.
Visit a nearby hobby shop, if possible, to buy your starter set. It's not only a magnet for like-minded local modelers and source of ongoing supply but also your go-to stop for answers to the many questions sure to arise as you progress. While you're there, pick up a beginner's guide to building layouts with sectional track. If a hobby shop is not available, Wm. K. Walthers (walthers.com) is one of the nation's largest online suppliers of model railroad gear.
Consider replacing the curved sectional track in your train set, probably18-inch radius, with 22-inch to increase your "minimum radius." Keep those two words in mind when you plan your first HO layout---or any layout. Minimum radius is the sharpest curve in your track plan. It dictates the minimum layout width needed to build a return loop and the kinds of equipment your layout can handle. HO's tightest radius, for example, is 15 inches---measured from the track center---so a curve needs more than 30 inches to build the 180-degree return loop that allows continuous running. However, only the smallest cars and locomotives will be able to go around a curve that tight without jumping the rails. Use a 15-inch radius only if there is absolutely no alternative, a 22-inch if you can, and an 18-inch if you must.
Plan on 22 inches, if space permits, because this provides a comfortable curve to turn around even larger locomotives and can be built with readily available sectional track. While most experienced HO modelers lay down yard-long lengths of flexible nickel-silver track, a newcomer is better off starting with pieces of fixed 15-, 18- or 22-inch radius curves and 9-inch long straight sections. HO track height is measured in thousandths of an inch, with .100 (called Code 100) the most likely size in your train set box. If it's .083, buy your 22-inch sections in Code 83.
Build your track plan by literally snapping together your track sections and following either a rough sketch of your own or a plan you like in the beginner's book. Plan to keep this first layout to a space no larger than four by eight feet. When you're satisfied with your track scheme, it's time to mount it on a base.
Go to the lumber yard and pick out almost any type of flat, precut surface: plywood, particle board, Homasote and MDF all come in 4-by-8 sheets. That size matches many of the starter layouts described in your book. If your track plan is smaller, have the dealer cut your 4-by-8 sheet to fit the layout size you designed. Even if you used 18-inch radius, generally considered the tightest practical HO curve, it can accommodate some fairly big rolling stock, though some larger locomotives may have been specially modified to travel the three-foot curves.
Transfer the rails onto your base and power them up, for the time being following the directions that come with your power pack. Later, you'll use a soldering iron to connect flex rails to a power bus, and break your layout into blocks or wire it for digital command control. But for now, let's get that starter train running around a loop. A good test for your trackwork is to back a full train through the entire loop, running in reverse at a moderate speed, to see if any cars derail. When you complete that circuit successfully, you've also completed an HO layout. It's not finished---by longtime hobby lore, no layout ever is---but it's certainly started.