That set of directions from the BMS manufacturer seems unnecessarily confusing. I've been looking at it for the past month, and I finally see how it works (I think). The BMS just goes inline between the battery and the motor/controller/charger, and acts as an on/off switch to stop current flow when necessary. Presumably those magic MOSFETs are able to control the voltage (or is it current?). I've redrawn it below the way I think it works.
http://www.buggiesgonewild.com/attac...1&d=1571832666