With regards to steering the aircraft while taxiing. On a lot of the larger jets (i.e. 747), the nose wheels are steered using a hand operated steering 'tiller' (via cables and hydraulic actuators), there is also an input from the rudder pedals, if I remember correctly, only active below 80 knots and only moves the steering by about 6 degrees, mainly used for keeping plane straight during the take off and landing roll. Some crews will use during normal taxiing for small corrections. Also on the 747 while taxiing, once the nose wheels go past a certain angle (20 degrees ?) the main body gear also steers, but in the opposite direction, to relieve the stress on the legs and assist with turning the rear of the aircraft.