Welcome to the board and the wonderful world of Lionel trains! It is a great father and son hobby that can last a lifetime.
The 2055 is a nice locomotive, with plenty of detail, smoke and a whistle tender.
You can use any track you want, but '027' and '0' gauge ''tubular'' track are being phased out by Lionel in favor of the newer Fastrack. Most hobbyists would agree that the '0' gauge track is the best with regard to being robust, especially the turnouts (or switches as they are called). Fastrack has some issues at times, one being that the trains sound very noisy on it, and the turnouts have occasional issues also, due to their complexity. As you are starting out with what is known as postwar trains, there are many operating accessories that can be had to add life and fun to your layout. Some, not all, of these older accessories do not adapt well to Fastrack, as they were designed before Fastrack was invented. '027' track is lighter, and makes a smaller diameter circle, and the larger engines and cars will not negotiate the turns and switches properly.
For powering up your trains, you will need a transformer, and lockons to connect the transformer to the track, along with wire. For a small layout with one locomotive and a few cars, an older 1033 transformer will suffice. If you are thinking of upgrading in the future to 2 trains on 2 separate loops, then you may want to invest in a larger transformer now, even if you do not have the trains now. A good, used KW or ZW transformer would be a good choice. Finally, you may wish to locate some smoke pellets, or liquid smoke fluid for your locomotive to get it puffing.
This should get you started in your hobby.
You may need to learn how to service your locomotive and tender to get it into optimum shape, including disassembly, cleaning and lubrication. Here is the service manual
http://pictures.olsenstoy.com/2055.htm for the loco to familiarize yourself with the terminology, and the internal workings of it.
Any old or new rolling stock will work with your locomotive, so you have a vast choice out there.
Enjoy your trains.
Larry