The out-of-the-box game's not really changed in 11 years, Kael's guide is still a good starting point (but was written for vanilla so doesn't include G&K and BNW features, like spy names and religions) but others in the Tutorials sub-forum do and are all still relevant. You still need to use tools from 2008/2011, but there are guides on how to install those on Windows 10/11 machines.
The best advice for modding is still "start small, add in increments" - if you try to make a total conversion with space ranger animated units on alien terrain as a first step you're going to struggle. And as always, pick another mod that's close to what you want to do (new unit/building, game play, whatever) pick it apart, see how it works and then modify it to your own needs.
And read the tutorial on how to enable logging - so you can work out what errors are yours and what messages can be ignored.