The circle of 5th (or circle of keys) shows the relationship between the various keys one can play in, and each subsequent key is a 5th away from the previous key (or a 4th away — depends on which way you move in the circle). For example, the key of C has no sharps or flats. To the right of the key of C on the circle is the key of F with one flat, while to the left of the key of C on the circle is the key of G. Each subsequent key has one more flat in the key signature (as you move to the right) or one more sharp (as you move to the left.) Watch the short video:

< For more information on the circle, please go to https://www.playpiano.com/101-tips/20-circle-of-keys.htm