The NeoPixel strand's data in pin is connected to pin 13 on the Feather.

One end of the USB power switch tail plugs into the Feather's USB port. Data and ground wires from the NeoPixel strip will get spliced into the USB cable's power and ground wires, and the other end of the USB power switch tail connects to the battery.

The LED seed pixels we're using can be tricky to wire up. They aren't generally marked, though if you look closely you can sometimes see a copper wire spooled around the +5v wire. Data is usually (but not always) in the middle, and it's difficult to tell which is the IN end and which is OUT. So, don't assume this diagram is correct for your pixel strand. We'll go through testing on the Assembly page.