It represented a line of music that God had His hand on. Remember what He said about Japheth - God was going to bless this line. Music is basically sound produced by vibrations. The faster and smaller string vibration, the higher the pitch goes. The slower the vibration and larger the string, the lower the pitch.
Pitch is the high and low sound.
The five-line staff was a developed idea. An established sound could only be played by one person until someone developed how to write it down. So a bunch of lines were drawn, and then an established pitch was designated, and eventually more and more lines were taken away, to where today, we have 5 lines representing the treble clef and 5 lines representing the bass clef. That staff that we use today took time to be developed, but it was developed through the Japheth line. Different kinds of notes - half notes, quarter notes, whole notes, etc. was also slowly developed over a long period of time.