Developing custom/user defined app on Pixhawk 4


I wanted to know how can i develop my own app and upload it on Pixhawk 4.

For now, I have refered to this page (Getting Started · PX4 Developer Guide) and I have got an idea about building simple apps for acquisition of data from sensors. But for doing something complex like accessing the remote control values , (values of roll,pitch, yaw, throttle) and generating pwm, accessing GPS data ,etc.

Need help regarding where can i learn about the library files and start coding?

All data can be readed using subscribers and choosing the right UORB message
check the liste of messages here :
example : to read RC channels, subscribe to the rc_channels.msg
to generate use publisher