I am getting into blues and don't understand somethings about the 12-bar blues. I was reading a page on it yesterday and it said that I should "Understand what it means to play a I-V-IV chord progression". Here I am totally confused because I've never seen "chords" in any of my 10 months in playing the bass. I used to play guitar so that idea of chords makes sense. But on the bass everything I've learned has been plucking individual notes, not chords as I understand them. Most of the blues bass lines I've encountered so far don't involve chords either, just specific notes. So in reference to the 12-bar blues can anyone explain to me what it means to play a chord progression?