Push & twist, very similar mechanism to a bayonet-fitting light bulb.
Three hooks go over three pins, then you turn it to lock.
I cannot tell from the photos whether the pins are in situ.
Just in case it's not entirely clear from that brief description, you lift the 'bucket' up underneath, it should fit outside the flange on the main structure. Then ...
Given this photo I found, it seems that the rod in your second photo is necessary. Unfortunately, I can't find alternate perspectives or an instruction manual. It would certainly not glue in, but it might push through allowing the bottom to hang. Then it could be removed to clean the ashes.