The fingers are numbered. The number of the finger that shall play the key is given in the falling keys (yellow stripes in the picture below). You shall press the key when the number reaches the piano (the red stripe).
If you do not yet have a keyboard or a digital piano, you can use the computer keyboard (letters and numbers correspond to the matching key).
In the front piano, the two middle octaves are presented. These represent the user interface; press the keys and you will move forward and backward in the menu system. There is a quickstart option. Just press one of the three black keys under "Quickplay":
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