Notation - key signatures
Key signatures show the key in which the music has been written. They are placed at the beginning of the stave.
The key of C has no sharps or flats
The key of G has one sharp (F#)
The key of D Major has two sharps (F# and C#)
The key of A has 3 sharps (F#, C# and G#)
The key of E has 4 sharps (F#, C#, G# and D#)
The key of F has one flat (Bb)
The key of Bb has 2 flats (Bb and Eb)
The key of Eb has 3 flats (Bb, Eb, and Ab)
The key of Ab has 4 flats (Bb, Eb, Ab and Db)
The pattern of a major scale is: tone - tone - semitone - tone - tone - tone - semitone.
Sharps and flats - known as accidentals - are used so that this pattern can be retained no matter which note you start on. Musical pieces are all based on scales, each scale indicating the notes that are available from that key for the composer to use. If notes are also used from outside the key, this is known as chromatic writing.
Key signatures and how they set the tone for a piece of music, with the use of sharps and flats