The final step is to put the electronics into the star. Simply place the NeoPixel/GEMMA bundle into the cylindrical recess in the star with the LEDs facing forward, plug in the USB cable, and then place the base model onto the backside, snapping the four posts into place. It should all hold together nicely via friction.
Plug the USB cable into a power source -- either a wall adapter or a battery -- and watch it sparkle!
All that's left is to top your tree with your rad 8-bit Super Mario star!