All tonal music is based on a major or minor scale. If the tune “Twinkle, twinkle little star” is played starting on the note C, the notes of a C major scale will be used. The note C will sound like the home note (the “tonic”) and, indeed, the tune finishes on a C. The tune could have started on any other note (C sharp, D, E flat, E etc.) but a knowledge of scales would be needed as some sharps or flats (black notes) will be required. When singing the tune there is no need to think about the sharps and flats: the singer does them quite naturally.