To simulate a trait of the real aircraft, the nose wheel steering and rudder cannot be moved when the aircraft is stationary on the ground. This is due to the increased friction that is acting on the nose gear when the aircraft is stationary and any excessive force applied to the rudder pedals could lead to a component failure. 

Once the aircraft is moving, you will have full and free movement of the nose wheel steering and rudder using the pedals.

Note 1: The PA-38 Tomahawk (MSFS) uses the same default rudder control assignments as all other aircraft in MSFS.

Note 2: Users of FS Realistic may wish to disable the "Prop wash" setting if experiencing difficulties with the rudder locking in once direction when taxiing the Tomahawk.