Tom,
The first thing I would say is to not let yourself get intimidated by the PG Music software. There is a learning curve to this stuff but if you approach it with an open mind and don't expect to be an expert immediately you will find BIAB extremely good for making your own songs and for making different versions of cover songs. Don't expect to make covers that are just like the original. A good way to learn the software is to wade thru the menus and examine each component and make a stab at figuring it out. Don't spend to much time on one thing. The idea is to get an overview like you mentioned.When you get stuck , ask here. I just did a quick google and found a couple of tutorials. While I think they should be helpful they were done for earlier versions so you need to keep in mind there have been changes made along the way. The PG Music site has tons of tutorials and FAQS to peruse so check there too.

Just a simple idea on styles is this: Think of styles as a combination of the genre, feel, beat, of a song. When you select a style it's probably a good idea to start by getting some what close to the original style of a BIAB song by picking a style that has similar characteristics. Example ZZJazz swing 8's 140 tempo. If you don't get to radical to start with it will be easier to see how the styles change the flavor of the song. Later on you can try totally different approaches. Don't discount that a style is country oriented. Sometimes you can get some fabulous results with country to jazz , Funk to Pop and so on. Styles can be broken down to to main categories. Real Tracks and Midi Styles. Midi Styles have been around for a long time and there are even 3rd party styles produced by people like Bob Norton of Norton Music.The Real Styles incorporating Realtracks are relatively new (a couple of years maybe). Anyway these styles effectively can replace the midi styles. I won't try to explain how they do it but essentially they have live musicians recorded . Then they are able to chop up the recordings and stitch them together when commanded by the software to produce tracks based on the chords you input or existing BIAB songs that sound more like real musicians playing instead of the tinker toy sounds you get with some cheap synthesizers.
Hope this helps get you started.
Bob Hunt

http://www.bernert.org/tutorials/binab/index.html
http://www.larry-bolch.com/band-in-a-box/

http://www.saxmagic.net