The key of C major was discussed earlier. A piece of music that uses notes from the C major scale is said to be in the key of C. Similarly a piece of music that uses notes from the G major scale is said to be in the key of G major. Music in the key of G will contain F sharp (F#) notes.
Instead of writing a sharp sign before every F note on the staff, it is easier to write just one sharp sign after each clef. This means that all the F notes on the staff are played as F#, even though there is no sharp sign written before them. This is called a key signature.
The C major scale contains no sharps or flats, therefore the key signature for the key of C major contains no sharps or flats.
The G major scale contains one sharp, F#, therefore the key signature for the key of G major contains one sharp, F#
Waltzing Matilde is the most popular and well known Australian folk song. It is in * time in the key of G major. Remember that the key signature indicates that all F notes are played as F#. Try accompanying this song both fingerstyle and pick style using bass notes on beats 1 and 3 of each bar. Play the F# note one the 4th string with four fourth finger. and the F# note on the 1st string with your second finger.
This is a flat sign.
A flat sign written before a note on the staff means that you play the note that is one fret lower than the note written. For example, the note written on the staff below is called G flat (Gb), and is played on the second fret of the 1st string. When a flat sign is written on the staff, it is always written before a note.