First of all, you'll have to cut out two rectangles (one a bit bigger than the other) to form the card. Choose two colors that will look beautiful together.
Of course you can draw your own template, but that takes a lot of time, so feel free to use the one I made :)
Copy the template onto your card (use a window!).
Now cut the full lines and fold the dotted ones.
Draw the keyboard.
You can make a little butterfly to watch over your piano :)
Voila, you're done :)