Hold the assembly in one hand, and slide the top piece into place with the other, with the text facing up.
This piece is optional, but we recommend you use it, since it will add substantial structural support to the whole enclosure. If you want to go on without it (you can always add it later), skip this step.
Now it's time to fasten everything together! Hold the enclosure on its side and insert one of the nuts. Insert a bolt through one of the side pieces and screw it in. Repeat this four times to assemble the whole box.
If one of the nuts falls into the enclosure, don't worry. You should be able to guide it out through one of the holes.
We'll assume you're ok with this, but you can opt-out if you wish.