Fixed gear bikes do not have gears; there is no cassette, no gear shifters etc. The chain is linked with the crank and the rear sprocket.
Our fixies come with a flip-flop rear hub, which means that by flipping the wheel, you can ride freewheel or fixed.
By riding fixed, you cannot coast - the pedals are always turning once the wheels are moving. It's like the days of yore when you used to ride down a hill with your legs sticking out in order to avoid being bruised by the rapid moving pedals! It provides a more fluid ride as you have to pedal constantly, and the cadence will provide great leg suppleness. Some cyclists prefer fixed for fitness, and for the challenge. You can also pedal backwards on fixed gear.
By riding free, the pedals work in the same manner as a geared bike; the pedals only move when you push them. So in essence, you can coast, and you only have to pedal when you need to. When riding downhill, the pedals are stationary so you can rest your feet on them. It proves for a more relaxed ride.