I think the basics are pretty simple and intuitive. You type in a chord progression, choose a style, and BIAB creates an accompaniment. (Of course you have to know what chord progression you want--so that assumes some musical knowledge!)

There are other aspects, including making your own styles, that look far more complicated.

I think BIAB (probably PGMusic in general) has never been very strong in the area of documentation however, which might be part of the problem had by the OP. I think better written user manuals could be helpful. (I found it strange too, that with new versions, a new full user manual didn't come with it, but only an "upgrade" manual. So, one might have to search one's full manual from several versions back, plus all the upgrade manuals since then, to find the answer to a question one had.)

(The 2009 HDD upgrade didn't come with a printed manual at all, and I haven't looked at the electronic ones yet, so I don't know if my comments above relate to the most recent version. It was strange in the past though, with each new version only to get an "upgrade manual", and to have to keep several upgrade manuals plus an original manual (from several versions back) for reference.)

I never found the manuals very well-written. But again, the basics of BIAB are pretty simple, IMO, without looking at the manual.