Unlike upright bikes, indoor cycling bikes (or spinning bikes), have a weighted flywheel which is connected to the pedals through a transmission system that closely resembles that of a real bike. Together with direct-contact braking to provide resistance.
You have to lean forward into an almost crouching position, as you would on an actual road bike. You can also adjust the handlebars, and the resistance via knob, like you would change gears. An indoor cycling bike allows you to pedal while standing up, which is an advantage over traditional upright bikes, as they require you to remain seated at all times. Pedaling while standing gives you a much more intensive workout and engages different muscle groups.