kindle
The Kindle modding guide is the holy grail for learning about making your own software modifications to the Kindle.
Because you (probably) don't have a device available with you to test, following the GTK tutorial will walk you through cross-compilation, resulting in a version of your app you can run on your own device as well as the Kindle.
You'll submit the generated binaries when you ship your project.
Modding a physical Kindle
The device you get from this YSWS may vary based on availability, but all should be able to be jailbroken through various methods. MAKE SURE YOU DO NOT TURN YOUR KINDLE WIFI ON BEFORE READING THROUGH THESE GUIDES!
Why? Each jailbreak version depends on the Kindle's current firmware version, and there's a chance that a new patch will be released preventing you from being able to jailbreak your Kindle. Keep it in Flight Mode unless the guide instructs otherwise.
a hack club ysws | open source at hackclub/tinker