Mark the inside of your garment where you want the buttons to go. Use a thread ripper or an awl to make 4 holes around your mark, at 12:00, 3:00, 6:00 and 9:00.
Use a needle threader or a beading needle to pull the wires through the holes. It helps to keep all the buttons oriented the same way (i.e. the red wire is always on the left).
Flip your garment over and pat yourself on the back for being consistent with your wire color coding.
Pull the green button wires out of the way for now. Then starting at the "in" end, hook up all the power and ground wires, then hook all the "out" yellow wires to the "in" white wires of the next button in line.
Hook up the power, ground, data-in and button wires coming from your first button to your tester Gemma once again. Be sure the whole strand comes on and reacts when you press the first button. Test the other buttons by hooking each green wire up to your gemma one at a time.
Once you're sure everything works, sew the buttons tightly to your garment through the remaining holes in the 3d printed cups. Be careful not to get thread tangled in the button workings!
Glue the caps onto the buttons using E6000 or epoxy.
Play with your clicky buttons and watch them twinkle!
You'll notice that the buttons respond very nicely to the first few presses -- the non-animated patterns. As soon as the neopixel patterns become animated the buttons don't respond as well. Neopixels don't like to be interrupted when they've been given a task, and the Adafruit Neopixel library's animated modes don't play well with button presses. We'll fix this by using the FastLED library and fancier microcontrollers in the next section.