Help with a Kreg pocket hole system

In advance, thank you for your help-
I know how a pocket hole system works in theory… but not how they are actually used. This matters because I went ahead and, at a garage sale, picked up this:

I have no idea if I am missing pieces or not. Clearly the previous owner mounted it to a table (the center part with the clamp and the two similar pieces on either side are mounted to the table), and that seems to make some sense. As for the rest of it, I have no idea how it all works together. Does anyone identify what model system this is, and if you know of a link to a manual that would be great. Any tips would be appreciated, especially 1) why there are these square-tipped drivers and 2) what size screws is this setup for?

Thanks again,
Alex

Source: http://lumberjocks.com/topics/40988

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