A mountain bike is a multiple speed bike designed for off-road and rugged trail riding. Unlike the traditional road bicycle ten speeds, the mountain bike has motocross style handle bars and thick treaded tires that lend themselves to sport ter maneuverability and grip on rugged trails. Any high end mountain bike will already come equipped with suspension, whether it has front end suspension, back end suspension, or both will be dependant upong which type of mountain biking you'll be using it for.
The first thing to ask yourself before buying a mountain bike is "what do I want use it for?" Bicycling is one of the most effective methods of cardio-vascular exercise if you are willing to commit. A mountain bike however is designed for rugged terrain; if you are interested in biking on pavement a road bike will be a sport ter selection and take you further, faster. If you are ready to get dirty and a little sore riding off road on some back trail than you are a born mountain biker.