Step 5: Glue the top and sides together
Locate two of your completed side panels and the top. With the top and one of the side panels, fit them together and then tape over the joint from the outside with a piece of masking tape. If you're careful to do it tightly, then it should make a pretty good right angle. Then, with the other side piece, apply superglue to the in-cut parts of the dovetail joint along one side. Then, just connect the pieces together.
(note: if you don't want to use tape, you can also apply superglue at the arrows seen in the picture, and then attach the three sides as shown. Everything should fit together nicely either way)
After pressing for a few seconds, the glue will have set, and your two sides should be joined at a very nice right angle. Now you can remove the tape and take the top off, then apply more superglue along the top edge of the two glued sides and actually glue the top on.
Congratulations, you've made a nice strong corner of your lamp! Now that you have this arrangement, it'll be easy for you to put the rest of the sides on. Note: do not glue the bottom on, only the sides!
Glue the other two sides onto the box, then stop and admire what you've made in front of a bright light source.