I'm a complete beginner in programming and would like to learn how to code and hopefully create a RAT.
learn lower level languages like c and assembly to really understand computer architecture. Look up resources online for actual malware development, and how to manage memory and pointers. Look into proccesses, threads, buffer overflows, binary exploits.
look at the "start here" tab. The programming language you choose all depends on what you want to build. do some research on what different programming languages are capable of or specialize in, then choose which one best suits what you want to accomplish.