It is as simple as it looks. You get a plastic bowl a metal bowl (or cake tin like ours) have a feel of them, which feels warmer? The plastic one right? The metal one feels colder. So which one will make your ice cube melt the fastest?
Now place an ice cube in each at the same time.
You leave them there and wait to see which melts first.
The one in the metal container right?
First of all when we felt the two containers the metal one felt colder. It's all to do with the way that the body feels heat and the rate metal conducts heat. If a room is at 21 degrees C all the objects in the room will eventually reach the same temperature 21 degrees C. A person standing in the same room will be (say) 36 degrees C so when that person touches something in the room they will be at a higher temperature than the object they are touching. That heat will flow away from the person into the object.
How quickly this happens depends on how well the object conducts heat. Metal is a great conductor of heat so it flows quicker, it takes the heat so quickly in fact the nerves in our skin senses it feels colder and therefore perceives that the metal is colder even though the metal is warming up.
It is also because metal is a conductor of heat so it will soak up all the heat around it and be warmer than the plastic bowl which doesn't conduct heat therefore works well as an insulator. Because the metal is warmer than the plastic bowl the ice cube melts quicker in it.
For more experiment go to An Ordinary Life's science page