1. The following line is played by the left hand, so it is a chord. The line above is the right hand playing the melody!

2. The treble clef can also be called the G clef. It started with the second line of the staff. The bass clef is drawn with the fourth line, which can also be called F clef. . . For example, taking "1" as an example, a lower plus one line is the same as an upper plus one line. But if it is another sound, it will be different!

3. This is key signature. For example, "b" is a flat key; A "b" is F major. . . Two are in B flat major. . . . . . .

five are in d flat major. . . . .

It's also possible that there is "#" and this is key signature in a sharp tone.