Step 1: Solder together some LED strips into a matrix
When you download the code from github, you'll see a folder called "examples". Make sure this folder is in your "Arduino" folder (NEXT TO "libraries"--NOT inside of "libraries"). Make sure you download NeoMatrix AS WELL AS NeoPixel and GFX, and put them all in your "libraries" folder. Check the image of my folder structure to make sure yours is similar.
Now that your code is in the right place, open "examples", and find "matrixtest". Open this file up.
You'll see, near the top, the line of code to define your matrix object. Here's mine:
Adafruit_NeoMatrix matrix = Adafruit_NeoMatrix(5, 7, 3,
NEO_MATRIX_TOP + NEO_MATRIX_LEFT +
NEO_MATRIX_ROWS + NEO_MATRIX_ZIGZAG,
NEO_RGB + NEO_KHZ800);
Here's what that code means:
Adafruit_NeoMatrix matrix = Adafruit_NeoMatrix( = "build me a new matrix"
5 = "that is 5 pixels wide"
7 = "and 7 LED strips tall."
3 = "I will plug my blue data wire from my LED strips into pin 3 on my arduino."
NEO_MATRIX_TOP + NEO_MATRIX_LEFT = "The beginning of my strip, nearest the arduino, is at the top left corner of my matrix."
NEO_MATRIX_ROWS = "I'm orienting my strips horizontally, not vertically."
NEO_MATRIX_ZIGZAG = "I'm soldering my strips in a zigzag pattern, not a progressive pattern."
NEO_RGB = "My strips have RGB LEDs, not GRB LEDs."
NEO_KHZ800 = "My strips work at 800KHz." (These last two will be on the data sheet for the LED strips you bought.)
Note in the picture that I have 5 LEDs per strip on 7 strips. My arduino is in the top left corner of the matrix. My LED strips are horizontal, and I soldered them together in a "zigzag" pattern.