How is Cessna 172 steered in taxi?

A Cessna 172 is taxied by use of the rudder pedals.

The rudder pedals are connected by rods to the steerable nosewheel. There is a certain amount of advantage of propwash over the rudder, but the wheel swivelling is the main steering method. You can also use differential braking, that is pushing on the tops of the rudder pedals, causes them to lean over and apply brakes. These are independant, so pressing the left brake, causes a turn to the left, actually tighter than the nosewheel circle. When the 172 has taken off, and the nosewheel oleo is fully extended, the wheel only swivels until it comes to the straight ahead position. Then it locks, and stays that way, until landing, and there is sufficient weight on it to unlock and the steering rods are active again.