It looks like a pretty foreboding process but most of it is setup pretty logically. There are areas that say “don’t modify this section” It’s pretty self-explanatory. There are really only 2 files you ever need to modify the config.h and the config_adv.h.
As someone that still follows the rule, Only modify one or two parameters at a time and compile to ensure you haven’t introduced an error you should be ok.
If you want to look at some good YouTubers on firmware look to Teaching Tech, Chris’s basement, and CHEP. All have a solid safe way of going about making firmware and will walk you through the process on a particular printer.
I will be honest though The most painful part is getting VScode set up and working properly, Just take your time, add the plugins that are recommended and the first time you load your firmware, Select your proper control board and try to build it right away with no options selected/Modified. once you get the first one to go properly rest is pretty easy.
Sorry for the long-winded answer but you will do well with it.