To use with the Arduino IDE, you will need to install the Adafruit_seesaw library (here's the Github repository.)
It is available from the Arduino library manager so we recommend using that.
From the IDE open up the library manager...
And type in adafruit seesaw to locate the library. Click Install
The library comes with a Joy Featherwing example to get you started fast. Plug the Wing into the Feather and connect the Feather to your computer with the USB cable.
Open the Arudino IDE and load File->Examples->Adafruit_seesaw->joy_featherwing_example
Click the Upload button and open the Serial Monitor at 115200 baud speed.
When you move the joystick you should see data appear in the format x,y
When you press a button, a notification should appear in the monitor.
If you'd like an all-in-one library that abstracts some of the FeatherWing for you, check out Leonid's FeatherJoyWing library https://github.com/leonidlezner/FeatherJoyWing