1. Open simpleShapeBase.mb.
2. Duplicate simpleShape128 with the input graph. Rename the new shape Col_1 and set its subdivisionsAxis and subdivisionsHeight to 6.
3. Open Outliner (Window > Outliner).
4. Expand base01. Select detail2 and duplicate it. Rename the new detail marker Collision_1.
5. Save the scene file as simpleShapeCollision.mb.
6. Export this shape. It will now have a collision mesh.
The easiest way to test the collision is to replace an existing shape in the game. For example, you can export a shape called bush1.dts and replace the one that exists in the demo (make sure you rename the old bush1.dts and have your texture in the same directory). Drop in the demo, and you can crash into and bounce off of the shape you just made.