Well, we could really use a lot more information, and some pictures would definitely help. But in lieu of that for right now........................
Put your track together on a suitable surface. The pieces probably form an oval, or maybe just a circle. There should be a "lock-on", a device that clips to the track. This allows wires from the transformer to hook up to the track. Then hook up two small wires from the transformer to the lock-on. Set your loco on the track, and plug in the transformer to an outlet. By moving the lever on the transformer, it will start feeding voltage to the track, and the loco should start moving. By turning the lever off and on, the train should start, stop, reverse, stop, then keep repeating this sequence.
This assumes that this is an A.C.-powered train (most Lionel trains are), the track is clean, the transformer is in working condition, the loco has a working reversing unit that cycles in a forward-neutral-reverse-neutral sequence (or it may have just a forward-reverse sequence, without any neutrals). The main problem is though, if it hasn't been run in over thirty years, it may need some serious maintenance before it will run at all.
Hope this helps for now.