Now next step is to plug in a VST instrument in order to get sound.
You can see it like this: the Bach part with the notes is like a score: it contains musical events, but a score doesn't make a sound from itself. It needs to be played by an instrument e.g. a piano, organ, bass, ...
So, in this case, we have to plug in an instrument in Rack A, because that's where the events of the part go to.
Do you know about vst plugins?
