On page 27 you were introduced to key signatures. A key signature consists of one or more sharps or flats written after the treble clef, or in the case of the key of C major no sharps or flats. Because the G major scale contains the note F#, the key signature for the key of G major will consist of an F# note written after the clef.
This is the key signature for the key of G major. It has one sharp sign after the treble clef.
The C major scale contains no sharps or flats, therefore the key of C major contains no sharps or flats.
It is possible to play any melody in more than one key. On the previous page you learnt this song in the key of C major. Here is the same song in the key of G major. Changing the key of a piece of music is called transposing. This process will be discussed in detail in lesson 17.