You have to find 4 objects that are shattered. After you assemble them, they can be ued to trigger actions in the scene. Also there's a certain amount of precious stones that you can collect and will give you extra points.
Click the pieces to assemble the objects; when one is ready, click on it to perform an action over the scene that will allow you to discover a mystery. For example, in the first level the first object is a dagger, and you use it to cut a red canvas that hides the content of a small niche. To collect the gems, click on them.