Circle of Fifths
The Circle of Fifths is an easy way to find out the key a song is in. The Circle of Fifths tells you how many sharps or flats are in a given key. C has no sharps or flats. It is called the Circle of Fifths because as you go clockwise you go up a fifth. For example, the fifth note of the C major scale is G. The fifth note of the G major scale is D, and so on.
The Circle of Fifths can also be used to help to learn chords. You already know that the Circle goes in Fifths clockwise. Now look at how close the chords that are a fifth apart are together on the fretboard. You might not use this too much, but it will give you a broader view of the chords and how they are related to other chords.