When Tomoko was a little girl taking piano lessons, she had to buy her piano books and sheet music. That is still the case for most pianists, although now those scores are sometimes downloadable from the Internet.
Basically, sheet music is just a way to codify music to allow others to reproduce it without having to listen to it directly and try to imitate it by memory. The first evidence of musical notation was found on a cuneiform tablet in Iraq. Later, papyrus and paper were used to transcribe music by hand.
Even with the advent of printing, usually just the staffs with its lines were printed; the notes had to be hand-drawn afterwards because the placement of the notes, along with lyrics, was so critical. Fifty years later, the other score elements could be printed too, but it took three “passes” of the printing press to get all the elements in place accurately. By the mid sixteenth century, the staff lines and notes could finally be printed in one pass.
As an alternative, the score could be engraved on metal plates, and then re-used for future printing, which was efficient for popular pieces; nowadays, photographic engraving is used. The music could be reproduced as a picture (like a photo), but that process assumed that a score was already produced. That was still a problem with the advent of the computer.
Since the 1980s software has been developed to enable composers to “type” musical scores with increasing sophistication, which could then be printed on a graphics printer. Now a person can play the notes on a MIDI device, and the computer will generate a MIDI file of sheet music. Some software programs include a play back feature so the composer can listen to the piece in development, which facilitates its refinement.
Nevertheless, even with the perfect piano sheet music, the actual performance is only as good as the pianist. There, Tomoko exemplifies refined technique and interpretation. The sheet music comes alive!