Hi Tater, to be honest, we are pretty new to milling as well, My brother just bought his mill about a month and a half ago. The easiest way to think of doing book matched, or mirrored slabs is when you cut a slab, as you are lifting the slab off the log, turn it over like you are turning the page of a book. Essentially, the underside of the slab you cut off, should be a nearly exact mirror image of the top of the remaining log. Once you cut the next slab, pair it up with the previous slab and now you have a bookmatched pair.
I think most people will usually just mill the whole slabs, and then use something like a track saw to make the straight cut to mate the boards to each other. We weren't able to do that because my brothers mill will only do about 21" diameter logs, and the one that all these slabs came from was about 34" in diameter. We had to cut the log into quarters with a chainsaw and then flatten the square edges with the mill before we cut slabs so we could determine how best to slab.
Hope this helps! Any other questions just ask and I'll do my best to answer.
