@Matt: Start Band in a Box, click Song (left of the Display for song title and style) - that opens the song picker tab in the multi picker - select a song title and double click, press return, click some apply button or what else: most of the times, nothing happens.
Should something happen? I'm not sure at all.

@DrDan: I'm not totally new to Band in a Box - as I said, I tried to use it many times, mostly to have some background changes while practicing guitar, e.g. just bass and drum of a ii V I sequence in different styles.
But as you say: They want to provide every possible way to do everything that might be possible, and that's just overwhelming, especially with this 'historically grown' user interface. But I don't want to open that debate here...

Concerning the song files: I somehow found out (with help of this forum) how to populate this list. As the preinstalled song files didn't make sense to me - I probably got something wrong here as well -, I packed it with the free files Bob Norton provides: The Realbook for BIAB and the files from the Independent Users Group.

And for your 'final warning': I'm extremly bad at distinguishing between misapprehensions on my side, bugs and weird features.

Anyway, I'm really thankful for your jumping in (I mean both of you)!