TOTAL NEWBIE to Pixhawk coding!

I am essentially an old school aeromodeller … so building planes no worries …
Used to do coding in C++ long long ago …
Autonomous flying’s caught my imagination so want learn how to code the PX4 like deep stuff
so where do i start ? do i learn ROS,…or Linux or what?
Do I go back to brushing up C++???
ADVICE ADVICE ADVICE… Sil vous plez!!!

It depends on what you want to achieve. First, it is advisable to learn to use PX4 as a user.

Done … PX4 being used for Fixed wing and Quad