Thank you, Ray. Since you're an experienced user of the Piano Roll, I'll describe my current situation and ask a true beginner's question:

I typed in a few random chords, changed to the Piano Roll view, and then grabbed various notes, moving the bars up and down.

When I hit the play button, however, I hear the same progression that I originally typed in, as if I had not changed any of the notes in Piano Roll. I DID hear the changed pitches when I moved the bars, but playback gives me an unchanged progression -- even though I can see the bars light up in their changed heights.

What am I not understanding about playback in the Piano Roll?