You have to solve a mystery by finding hidden objects; at each level you have a list of objects to be found. Sometimes the list describes the objects in an elliptical way, like: 'the shape of Italy' to say 'boot'. When you're stuck you can use the key to find at least one object.
Click at any object that you find at the scene and is included in the list. If you click needlessly or wrong you'll lose 20 seconds.