The RGB LED has 4 pads -- R, G, B, and +. The PropMaker Wing has matching pads in the center of the board. 

The PropMaker wing will stack on top of the Feather M4 Express, and the battery pack plugs into the Feather.

Important Note about Power!!

Do NOT leave the battery pack plugged in to the Feather while you also have a USB cord plugged in. The Feather has onboard charging, so it will try to charge your AA batteries, which could result in battery damage and / or Feather damage.