Locomotive
Your first step in setting up a quality HO train track is to find a great locomotive. You will spend more money on the locomotive than on any other part of your train. Like on a real train, the locomotive pulls all of the other cars, so you need a locomotive that will run smoothly and not quickly break down.
Electricity powers your locomotive. It runs from your power pack through the train track and into the wheels of your locomotive, where it is then wired to the locomotive's engine. Because the wheels are used to pick up power from the track, one important feature of your locomotive is having many conductive wheels. Cheap locomotives have only the front or back two wheels made out of conductive metal and attached to the motor, while better locomotives use all of the wheels to pick up power. Also search for a locomotive with a powerful and durable engine that can fully utilize the electricity.
Power and Tracks
After purchasing a locomotive, the next step of of setting up your HO train track is finding a power pack and track segments. The power pack moves electricity from an outlet into your train track. You should find a power pack that sends enough electricity to fully power the locomotive that you chose. Ask the owner of your local hobby store for help finding a power pack to match your locomotive.
Model train track segments come in to styles: with a base and without a base. Tracks with a base snap together easily, and rarely have problems maintaining a circuit. On the other hand, the bases look more toy-like than tracks without a base. Most model train hobbyists eventually use tracks without a base. If you are willing to upgrade to a new track after learning more about model trains, then start with a track with a base. If you want to continue using the same track as your hobby progresses, buy a track with no base.
Accessories
Since HO is the most popular model train scale, you will have no trouble finding accessories to match your locomotive and track. The first purchase you will likely make is a set of additional cars for the train. The train looks much more impressive when it has more than just a locomotive. You can also find all kinds of scenery to enhance the look of your track's layout.