Why is this on HN? Because there is a giant overlap between hackers and musicians.
For those of you interested, but confused, go to a music store and ask for a "fake book," a big collection of tunes in "head chart" format (just melody and the kind of chord symbols being discussed here. Study it like a new programming language. Bang out the chords on a piano, if you can. (Most fake books have a "glossary" of the chords in the front or back.)
Donald Knuth said that when a new CS grad student arrived at Stanford, they didn't ask, "are you a musician?," they just asked, "what instrument do you play?"