Applying forces or torque to a dynamic simulation

Hi,

I'm designing a simulation in Mechanical Design Experience.

I understood the excitations (position, velocity, gravity), and the springs. But, I need to apply a force on a part (It could be a force or a torque). How can I do that ?

For instance I would like to apply a force on a piston to make it move a mechanical system (like in a pneumatic gripper).

So my question : is it possible and how ?

thanks a lot for help !