The one way bearing is located inside that hex shape bit that fits in one of the spur gears (if my memory is correct please correct me if not).
It should work in the same way as the back wheel of a pushbike. i.e it should turn freeley in one direction and in the other direction it should lock and turn the shaft its on. This allows the cluth to engage on the higher ratio gear and turn the shaft faster as it then "freewheels".

Hope this helps.