How many types of tractor are there?

Several. Lawn tractors are small, riding lawnmowers. Garden tractors are larger and can handle more implements. They come in two wheel drive and four wheel drive. Four wheel drive articulated machines are split in two halves, connected at the middle by a hydraulically operated hinge. They turn by pivoting on this hinge rather than turning their front wheels. Some have tracks, while others replace their tires with crawler units.