Each of the keys on the NeoKey 5x6 Snap-Apart are the same. The board can be snapped apart to make a matrix of any size 5x6 or smaller. The traces run through the snap-apart bits and pass the power, NeoPixel, and keymatrix lines up and down. Below are the pinouts and features of each individual key.
Each key has a Cherry MX or compatible key switch socket. Simply press any compatible key switch into the socket from the top of the board. You can add a dab of glue to keep the switch in place; hot glue or a dot of epoxy will work.
At the bottom of each key is a NeoPixel LED. These LEDs are reverse mount, meaning they're mounted on the back of the board to shine through to the top. This allows for the key switches to sit flat while still providing rainbow goodness! The pins labeled I or IN are for sending the NeoPixels data. The pins labeled O or OUT are for wiring to another IN pin (to connect a separated matrix, or a second 5x6 sheet).
The NeoPixel LEDs are in a zigzag order across the board, beginning at the upper left corner and ending in the lower right corner. If using the full sheet, the "strip" follows the arrows in the image below.
The I and IN pins are the NeoPixel data in pins for sending data to the NeoPixels from a microcontroller, etc.
The O and OUT pins are the NeoPixel data out pins, for connecting to the data in pin on another set of NeoPixels.