You have to turn on collision detection for the scene . Its the buttons on the right of the preview display.  One mode is to show collisions only, the polygons change color if they are in collision . The other mode prevents the collision and backs off the dial setting so the part just collides. It wont move any prop so you cant really push something. And it does not work in animations, except at the keyframes.

If you hover over the buttons you should get a test window showing what the button does.