Making apps for the Flipper is phenomenally simple. You don't even need to make a Makefile: it's all in the application.fam manifest. The API is very well documented here and there's plethora of sample applications and tutorials out there - for instance, this one which is pretty good and got me started.
What you do need however is a somewhat solid knowledge of the C language. Not C++, not C#: plain old C. But you know what? I reckon getting started with your first Flipper app would be a great way to learn C. It's easy, it's forgiving and it's very quick to test changes and debug what you're doing using the CLI log.
Give it a shot: it's honestly a great and rewarding little platform to develop on.