In order to integrate the Core1 hardware you’ll need a URL to paste into the preferences file. If you copy it now, then you can follow the instructions after the link and paste it in.
The wonkystuff Boards Manager JSON URL is:
https://wonkystuff.github.io/arduino/package_wonkystuffPlatform_index.json
Here are instructions on how to add 3rd party hardware to the Arduino IDE
Once you’ve added the URL to the preferences page, you’ll need to install the wonkystuff board package.
In the Arduino IDE, select Tools -> Board <something> -> Boards Manager…
At the top of that window, type wonkystuff into the filter text box. You should
now see Wonkystuff Core1 - click on the text and then click the install button.
After a short-ish time, this should be done and the boards manager window can be closed.
Now in the Arduino IDE, select Tools -> Board <something> -> wonkystuff boards -> Core1.D (audio bootloader)
That’s it. With a test sketch (empty, or blink for example), click upload and the program should compile and then play the generated code through your computer speakers.