We'll be focusing the Feather line of boards, but the process is the same if you're using an ItsyBitsy, Trinket, Metro/Arduino Uno or any other microcontrollers, breakout boards, etc.
Adafruit Feathers are a complete line of development boards that are both standalone and stackable. There are over a dozen different boards with varying specialties, and each can be paired with a host of different FeatherWing add-on boards, so there’s a combo for just about any project.
Don't know where to start? The Feather M4 Express is a great basic board to begin with.
FeatherWings are boards with fancy add-on features that attach to your chosen Feather board. Some FeatherWings have sensors, or extra memory, or NeoPixel LEDS - the list goes on and on. All the FeatherWings work with any Feather board, so there are thousands of combinations available. My favorite is the NeoPixel FeatherWing. Search the store to see all the options.
You can use just one FeatherWing, or you can get a little extra and use Adafruit’s FeatherWing doublers or Triplers to add multiple wings to your project. The sky's the limit.
Once you've chosen your Feather and your FeatherWing, it's time to decide how to attach them together. This is where the headers come in. This guide will cover three main types of headers: male, female, and stacking headers. Some feathers also ship with specialty headers for attaching servos, connectors, or screw terminals. Once you've got the basics, those will be a snap to figure out.
Male headers are the "standard" headers that ship with most boards. They attach to the underside of the board so the plastic spacers are flush with the surface, and the solder joints go on the front of the board.
Female Headers have plastic sockets with short legs coming out one side. They attach to the top side of a board, with the plastic flush with the board and the solder joints underneath, on the back side of the board.
You can then plug a board with male headers into the female sockets and the two boards will be connected.
Stacking Headers are kind of a combination of male and female. They have a socket with long pins coming out. They sit on top of the board with the long pins sticking through the holes. The solder joints go underneath the board, and the long pins can extend down into another stacking header or female socket, or into a breadboard or perf board. As the name implies, you can stack multiple boards one on top of the other with these headers.