It is really very simple. You can play it at the piano or away from the piano (I have a little keyboard printed on the sheet to use if you are not at a piano). I put the sheet and a small envelope inside of a file folder for easy organization. Here's a photo:
The child gets to reach in the envelope and pull out a little picture. It could be a picture of a fish, a star, a butterfly, a rocket, etc. We then talk about if the object is high or low - a fish would be LOW because it swims deep down in the ocean. An airplane would be HIGH because it flies high in the sky.
Then we play some notes to represent the picture! My son likes to put the picture on the left side of the piano if it is low, and on the right if it is high.
The fun of this game is the improvisation that naturally happens when you start to play what things "sound" like. For example, when a child pulls out a picture of raindrops, you can start up high (where the clouds are) and play short rain drop notes going all the way to the bottom of the piano! A rocket ship can start low, and then when it "blasts off" you can play a fast glissando all the way to the top! A swing goes up, then down, then up, then down. The possibilities are really endless.
I love this because it gets the child playing and exploring on the piano! My son and I love playing "train music." One of us plays short, low "chugga chugga" notes and the other plays high, long "train whistle" notes.