Circle Of Fifths 
The Circle of Fifths is a memory aid for learning all the keys. Here are some fundamental observations:
Clockwise direction shows all the sharp keys
Anti-clockwise shows all the flat keys
Both directions start at the key of C major which is 12 o’clock
C major is the only key that has no sharps or flats
Clockwise ends with the key of C sharp
Anti-clockwise ends with the key of C flat
C, C flat and C sharp use the same notation letters
Each successive "hour" clockwise adds a sharp
Each successive "hour" anti-clockwise adds a flat
The name "circle of fifths" refers to the interval between the root note of each successive scale in the clockwise direction.
Anti-clockwise the root note of each scale forms the interval of a fourth with the root note of the following scale.