What is The symbol at the beginning of the staff that identifies a set of pitches?

Answer 1

treble or bass clef
A clef. All clefs indicate the pitch of a single note, and because note names are in alphabetical order, you can work out the other ones as well. The treble, or G, clef indicates the position of G above middle C; the bass, or F, clef indicates the position of the F below middle C, and the C clef indicates the position of middle C itself. All of these clefs are theoretically movable, and in fact historically they were placed on different lines (and they always do indicate lines, not the spaces between them). In modern practice, however, only the C clef moves. For viola players it's on the middle line of the 5-line staff (or stave, in British English usage), while for the higher range of the 'cello it's on the second to top line. The treble clef nowadays always indicates its G on the second to bottom line (in fact, its shape derives from the letter G), while the bass clef, which derives from the letter F, shows the note on the second to top line.