I installed NextCloud successfully on an Ubuntu 20.04 system. Everythings appears to work fine.
I’d like tinker with NextCloud source code a little bit just to see what can be done.
You can found also the source code on Github.
Your source code is in your installation path e.g.
And then the directorys e.g.
I strongly recommend you to not modify any source code directly. This might break unexpected things and the changes might be overridden on any upgrade.
Consider studying the developer documentation to incorporate your changes via proper APIs instead.
I understand. Just to get started is there an example using API doing a “Hello World” -type of app?
As answered here there is a complete tutorial to create an app from scratch in the developer documentation i linked above.