Starting from this scene, the collisions are easy to configure, as shown in the following screenshot:

For Chapter 3, Create, Load, and Draw 3D Objects on the Screen, let's zoom on the Babylon.js properties, as shown in the following image:

First, click on the options button (at the top) and for the selected object, which is the cube here, enable the collisions by checking the Check Collisions check box. For every mesh, check the checkbox to enable the collisions.

Now, let's configure the camera in Blender. Select the camera in the scene, click on the camera's options (at the top), and check the Enable Collisions and Apply Gravity check boxes if you want to apply gravity on your camera, as shown in the following image:

To configure the camera's ellipsoid, a BABYLON.Vector3 dialog...