////No mention of F in josepp's chart, which goes

C       D       Eb       E       G       Bb////

First, sorry, Al, for the bad condition of the chart. The Mudcat software scattered it up and wouldn't prints parts of it and so it just looks like shit and so I understand your confusion and I am sorry for that. It's damned near impossible to use without the headers of the chart which wouldn't print off correctly so I had to eliminate them.

C is the root, D is the 2nd (passing note), Eb is the minor 3rd, E is the major 3rd, G is the 5th and Bd is the 7th. Now you wouldn't play all these at once. The passing note is only play with the minor 3rd chord (which would be C Eb G, in this case). And these relationships are true of each row--root, passing note, minor 3rd, major 3rd, 5th and 7th.

This chart enables you to construct majors, minors and 7ths and to use the passing note with the minors if you are inclined to do that (which depends on whether it embellishes the piece or not). It sounds a little off from the other notes and the circle of 5ths shows us why--the other notes are next to each other on the circle but the passing note skips a spot. Why use it? It introduces a nice effect in the right context. Jazz bassists use it all the time. I imagine (but am guessing) that the more musically astute folkies use it at times as well. I suppose Will Fly or Don Firth can answer that. I can't.

There's no F in the sequence because F isn't part of the C major, minor or 7th chords. Now this chart is not dependent on the circle of 5ths. Really, you don't need to know what the circle of 5ths is to use that chart BUT the circle of 5ths shows you WHY that chart works.

Any note on the circle can be the root or I. The note directly to the counterclockwise is always the IV or that root. The note directly to the clockwise of the root is always the V. Then it alternates every other note to the vi and vii (lower case because they will always form minor chords which I, IV and V will always form major chords). That's why I told you to copy that one link that shows those relationships on the circle because that particular scheme is very useful. It's not mine but kudos to whoever came up with it.

When I first learned the chord layout of D G C F Bb Eb Ab Db F# B E A Eb Ab C# F# B E A D G C F Bb, I had no trouble memorizing it because I already knew my circle of 5ths and this layout basically follows it in reverse (technically making it a circle of 4ths). Look at the beauty of it: two consectuive notes in the sequence are the ii and V of the scale of the note to the right of those two--DGC GCF CFBb FBbEb and so on. And that's how it's laid out on the circle. ii-V is important to know because it is so musical that you can redo almost any song in this format to make it sound bluesy-jazzy-sexy. Whenever you hear someone cover a song in a way that makes you wonder, "How'd he come up with that sound?" That's how. He used the circle of 5ths. It is the secret to making music sound musical.