How to use MIDI and MuseScore

Thanks for explaining. That's an extremely difficult task for a computer, especially given that once you start playing a note, neither you nor the computer know when it's going to end. Your piano-like synthesizer probably can produce a midi file that will allow you to feed it back into the piano and reproduce the same sounds. MuseScore can indeed read such files (in the way I said), and attempt to impose meter and order on it, but this is a chancy proposition --- no program can read your mind. Even the playing of skilled classical professionals is rarely exact enough for a computer to "really figure out" what the "correct" timing is, let alone more subtle aspects of notation (worst case -- voice crossing). "The exact way you play it on the piano", to the millisecond, is easy to reproduce in score --- just "import midi", but as you'll find out, it's rarely close to what you really have in mind; it does not look like published music. This is a difficult problem.

Right now I'm trying to transcribe a 1955 organ improvisation from an MP3. I can never be sure if the artist really intended a short or long measure, or just lost count, or whether the dissonant note is really what he intended, etc. (and I have sufficient knowledge of the idiom to do a passable job of reading his mind, but only passable). A computer could not do it at all (of course, there was no such thing as midi 65 years ago). This is a difficult problem. Can you say for sure that your own playing is more metric/metronomic than that, or that you really know what the score you want looks like?

Maybe all you want is a midi transcription of what you play. If your piano/synth can't do this by itself, there are programs (MuseScore is not one of them) to which you can plug in your piano/synth and say "record", then start playing, then finish playing and press "stop" and it will make a MIDI file which, technically, satisfies your goal of "get the music from the piano to my computer". And you can email it or play it back any time. Midi is ideal for that; it is like a piano roll. All it cares is the timing of note starts and note ends (and for better keyboards, how hard you hit it ("velocity sensitive")). If that's your goal, it's very easy.

But the matter of producing a score that someone can look at and understand or play from is a wholly different, and very difficult, problem, especially if the person improvising did not try to keep to regular and understandable rhythms, and rarely doable automatically.