Are there documentation, tutorials or examples?
'StCAD' is an extension of GF/ST, so its documentation (gfstvw.hlp) is relevant. Class CADApp has some documentation in class methods. Class StMathHelp has examples of use for StMath.
Inside 'freeCAD', documentation are collected in a series of menu items labeled 'Explain'. Click on them anytime. But you MUST run the tutorials to learn 'freeCAD'. Click Explain/Quick Start/ for a list of examples on projectiles, circular motion, relative motion, pendulums, spring-masses, four bar linkages, piston crank, gyro, cam follower.
The motion simulation theory is in the journal paper:
Koh, A-S., and Park, J-P. "Object Oriented Dynamics Simulator," Computational Mechanics, Jun 1994, 14(3) 277–287.