Where do you put multiple washers when you have a bolt and a threaded hole?
Slip the lock washer on the bolt, then slip the large washer on the bolt, then screw the bolt into place.

The lock washer "bites" into the bolt head and into the large washer so that the two become connected. 
The large washer has a lot of friction against the bed post, so the bolt does not turn and back out.