We'll wire the NeoPixel strand to the Gemma as shown: the red wire goes to VOUT, the IN end of the middle wire to D1, and the remaining wire goes to G.
We could connect the power and ground wires from either end of our NeoPixel strand, but the middle data wire must be connected to the IN end or the lights won't work. It can be a bit tricky to tell which end is IN and which is OUT on these pixels, but if you get your magnifying glass out and look really closely, you'll see a tiny red or green dot on each pixel. The dot isn't perfectly round - it has a pointy end which points in the direction of data flow. So be sure to connect to the end with the tiny arrows pointing away.