Download Adafruit_IS31FL3731 library

To begin reading sensor data, you will need to download Adafruit_IS31FL3731 and Adafruit_GFX from the Arduino library manager.

Open up the Arduino library manager:

Search for the Adafruit IS31FL3731 library and install it

Search for the Adafruit GFX library and install it

If using an earlier version of the Arduino IDE (prior to 1.8.10), also locate and install Adafruit_BusIO (newer versions will install this dependency automatically).

We also have a great tutorial on Arduino library installation at:
http://learn.adafruit.com/adafruit-all-about-arduino-libraries-install-use

Load Demo

Open up File->Examples->Adafruit_IS31FL3731->featherswirldemo and upload to your Feather + CharliePlex Matrix Feather

At the top of the sketch, find the code that says

// If you're using the full breakout...
Adafruit_IS31FL3731 ledmatrix = Adafruit_IS31FL3731();
// If you're using the FeatherWing version
//Adafruit_IS31FL3731_Wing ledmatrix = Adafruit_IS31FL3731_Wing();

// If you're using the full breakout...
Adafruit_IS31FL3731 ledmatrix = Adafruit_IS31FL3731();
// If you're using the FeatherWing version
//Adafruit_IS31FL3731_Wing ledmatrix = Adafruit_IS31FL3731_Wing();

and uncomment the last line and recomment the second line so you have:

// If you're using the full breakout...
//Adafruit_IS31FL3731 ledmatrix = Adafruit_IS31FL3731();
// If you're using the FeatherWing version
Adafruit_IS31FL3731_Wing ledmatrix = Adafruit_IS31FL3731_Wing();

// If you're using the full breakout...
//Adafruit_IS31FL3731 ledmatrix = Adafruit_IS31FL3731();
// If you're using the FeatherWing version
Adafruit_IS31FL3731_Wing ledmatrix = Adafruit_IS31FL3731_Wing();

Upload to your Arduino, you'll see the LED display swirl different brightnesses!