What is the black key on the tone piano used for?

The black key on the tone piano is a semitone. For example, there is a black key between do and re, which is a semitone. Generally speaking, this sound is a little higher than the pitch of do, and is lower than the sound of re.

In the beginning of each line of the scores of some scores, the marks are similar to # and b. In this case, the sound at the same position as  is going to rise, and b is going to drop. For example, # in the fourth and fifth, explain all the fa in this line, which is not used to which fa should be raised by a semitone, that is, where you need to play fa, do not play the original fa, but to play the right side of fa Black key. The other case is that if # and b are only on the side of a note, only the note is raised. b stands for lowering, the same as above.

According to the position of the keys, the scale is like this, do, #do(b re), re, #re(b mi),mi,fa,#fa(b so),so,#so(b la),la , #la(b si), si means that the black key between do re can be said to be a rise do, or it can be said to be a drop of re, and so on.