D&D is a bit like Monopoly in that very few people play by the rules as written and instead most tables play by a semi-unique/regional subset of the rules and with a mixture of house rules and DM preferences. Especially people who have been playing for years, not only have they had more time to house rule and build DM opinions, but they also may have seen multiple versions of the rules over that time and interacted with a wider variety of other tables.

To some extent, this is weirdly a good thing: if you want strictly enforced rules, you may just want to play a videogame instead. D&D succeeds best as a social lubricant enabling a framework in which social gaming (roleplaying) can happen to be "fun". Rarely is strictly following rules "fun", especially socially with friends; the rules in D&D are meant to be guideposts and tools for enough structure that people that want structure find comfort and enough flexibility that "fun" isn't lost in the process.

Which is a long way to say that you probably aren't going to learn the right lessons from a well fuzzed computer spec of the rules, you probably are going to learn more lessons asking the people you play with what rules they find important, to explain things you feel you don't understand, and to suggest which chapters in which books to try to read to best improve your understanding for that group. At the end of the day, if the table seems too hard to play at you might also just be playing with the wrong group, especially if you aren't having fun.