To create the torsional load on the end of a shaft: Create a datum point at the centre of the shaft end which is to be loaded. Create a Force/Moment Load on the shaft end, and pick the shaft end surface. Click the Advanced button, and change the Distribution pull down to "Total Load at Point". Pick the datum point created above, and specify a Moment Component load using the co-ordinate system axis which runs along the shat axis.
Mechanica only measures cartesian displacements of the P-Elements. If you want to measure twist angle in degrees, create a displacment measure (magnitude) on a point on the edge of the shaft called PNT_DISP. Now create a Computed Measure using the following formula (where 200 is the diameter of the shaft at the measure point): (360/pi)*(asin(PNT_DISP/200)) This will give you the twist angle in degrees