It's important to choose the bike that's right for you. It depends on your fitness level and on where and how you'll be riding. This article looks at road bikes, mountain bikes, hybrids, kid's bikes and retro bikes. Future articles will look at electric bikes (e-bikes), tandems, recumbents and indoor exercise bikes.
A road (or racing) bike is, just like the name suggests, designed to go on the road or on a racing track.
You should chose a road bike if you're an adult or teenager and are intending to do your riding on a hard, paved surface such as a road.
Or if you are interested in competing.
Check out this definition from Wikipedia (click to access).
A road bike is characterized by a number of variables, starting with the frame. The frame's geometry lends itself to the rider's body being fully extended when their butt is on the saddle and their hands are on the drops (defined further down). Furthermore, the frame is light, to assist with sprinting (a high power to weight ratio) and hill climbing (lower weight) and rigid (to minimize power loss through flexion). To this end, serious road bike frames are made from carbon fiber.