Two shorter center pieces should go together and slot into the center slot. The higher angle is towards the back.
The engraved outer side slots into the outside hole on the bottom piece. The opening on this piece should be facing towards the ‘front’. The other side piece should sit beside this, again the higher side of the angled pieces should be facing towards the back.
The end piece with the ‘hole’ is the back pieces, this should slot downwards, you may need to push the side pieces together so they line up with the slot, slide it in part way without using too much force. This is repeated on the front side that is a little shorter and has no hole in it.
Once both ends are part way in with all parts lined up in the slots you should be able to push them down (if everything is lined up they should go in easy, but as long as it is seated in the slot using force downwards here is fine.) This should lock it all together.