The 5th note is the dominant as in the key of C that is G, counterclock wise the F is subdominant or the 4th note, in G the C is the 4th and D the dominant. Clockwise are the sharp Keys, while the left side cancels the sharp notes making them neutral notes while those notes that are not sharp are flattend. Meaning the B has 5 sharps except B and E. B flat major has 2 flat notes the B and E and the sharp ones are canceled makin them neutral notes. The major scale intervals are the cause of the flat and sharps of notes in a given scale. Applying the circle of 5th to a song means adding more chord and notes to make it more desirable to the ear. Key of G plus the chord F#minor derived from the 6th note of G and B7 taken from the 6th note of G is an example of this additions instead of going from G to Eminor. With regards to arpeggios or neo classical, an Aminor chord is played A C E in the key of C and an additional note is added which will lead back to A note. Likewise applying a diminshed scale to a secondary dominant which is derived from the 6th note, the guitar player uses a diminished scale to resolved to the 5th chord.
Frankly I haven't applied this Circle of 5th fully to actual use specially to songs. If there are mistakes kindly correct me.
retired employee 2012 , widower 2015 , Three grandchildren , Study Guitar .