In music, the key signature tells you which notes are supposed to be
sharp or flat. The key lasts the entire composition unless the key changes
somewhere in the composition. The only thing that can alter a key signature
(other than a key change) is an accidental.
The key of C has no sharps and no flats. The key of F has no sharps and one flat
(Bb). The key of Bb has no sharps and two flats (Bb and Eb). The key of Eb has
no sharps and three flats (Bb, Eb, and Ab). The key of Ab has no sharps and four
flats (Bb, Eb, Ab, and Db). The key of Db has no sharps and five flats (Bb, Eb,
Ab, Db, and Gb). The key of Gb has no sharps and six flats (Bb, Eb, Ab, Db, Gb,
and Cb). The key of B has five sharps and no flats (F#, C#, G#, D#, and A#). The
key of E has four sharps and no flats (F#, C#, G#, and D#). The key of A has
three sharps and no flats (F#, C#, and G#). The key of D has two sharps and no
flats (F# and C#). The key of G has one sharp and no flats (F#).
This picture was taken by Caitlin.
For more information about keys, visit this site: http://www.teoria.com/reference/scales/05.htm