Step 2: Burn Holes and attach battery
There should be 3 holes in the plastic, not 2 like the picture. I burned through the plastic using my soldering iron - a horrible idea, but there was nothing else around. it works.
Insert batteries into the battery pack. Tape it to the bottom of the plastic lid and loop the wires through the holes. The positive wire from the battery pack (usually red) should stay on the top side of the plastic, while the negative wire (usually black) should loop through the second hole back to the side with the battery.
Using a tape measure, make a small mark on the edge of the lid about every 2.25 cm (But it will depend on the circumference of your lid and how many LEDs you have. To figure out how often to make a mark, do the following:
Circumference of the lid / Number of LEDs
This is purely aesthetic; if you don't care about your LEDs being evenly spaced or just want to eyeball it, the device will still work.