I’ve seen that many professionals programmers use links from this website. Should I start going there? It’s confusing.
It’s the standards body for the world wide web, so
Well, yes, it’s the canonical reference. No, you don’t have to learn it (though note it has multiple how-to articles and examples hosted on its site, but I’ve rarely seen those referenced anywhere), in the same way you don’t need to look at the international standards organisation reference on weight if you want to measure yourself on the bathroom scales (but if you want to know the current definition of a kilogram, you may refer to ISO standards documentation). It’s for reference, so if you need to check the standard of how something is supposed to work, then it is the primary source, which is why you will see people linking to it.
Agreed, it can take some time to get used to how to read the standards, but that comes with experience. If you are serious about accessibility then it is indispensible.