Take a square sheet of paper, fold it in half sideways to make a crease and unfold.
Fold the side parts to meet the center line and unfold.
Fold the paper in half downward.
Fold the top corners downward to the lines of the previous creases and unfold.
Open the side parts, making their edges meet the center line.
Fold the central part upward in half and then fold upward again to make the keyboard.
Fold the side parts towards each other to make the piano walls.
Unfold the keyboard.
Draw the keys, and the piano is complete!