Here is a short melody created from the C major scale. Many of the melodies you already know will use notes derived from the major scale. This example is written on the treble staff only. Male singers can sing the same melody one octave lower at the same pitch as the male singer on the accompanying audio (second time through).
This is called octave displacement, and can be indicated in written music by the symbol 8vb which indicates that the part is to be sung or played an octave lower than written, or 8va which indicates an octave higher than written.