Can the circle of fifths help me learn to substitute chords?
Not really. It is more for chord progressions. Chord substitution is a personal, depending on song genre, and tricky thing. Here are a couple of things that may help:
http://i.stack.imgur.com/Hjuz5.jpghttps://www.bing.com/images/search?q=Chord+Substitution&form=IRMHRS&first=1&tsc=ImageBasicHoverIf you need help in chord substitution you would have to post the current chord progression as well as the genre. It makes a huge difference in substituting chords for a folk, country, or jazz song.