If I've understood correctly, then I just wanted to add that "part markers" are very easy to add - in the chord window, just click on the bar number (just to the left of where you enter a chord) and it will become blue and say 1a or whatever bar you're on. Click again and it cycles to 1b - keep clicking and it cycles off.

a's are usually less intense than b's - so it usually works to start verses with a's and choruses with b's...

biab also inserts occasional drum fills on the bars just before a part marker and sometimes a crash on the new part bar - so this is a way of adding dynamics and punctuation to your song...