Welcome James,
Anybody can propose changes to the Mendix documentation because all is on Github. How everything works is explained here: https://docs.mendix.com/community-tools/contribute-to-mendix-docs/
And you do not need to use any category. All post will end up in the Questions sections. But if you are looking for specific questions on topics the sections are sometimes more usefull.
And just go to the Mendix academy and with your background start the crash course: https://academy.mendix.com/link/paths/82/Crash-Course
Regards and happy coding,
Ronald