The crucial thing we unfashionable types tend to ignore is that our own appearance is also communicating lots of things about us, all of the time. There's no way to opt out of this program, any more than an illiterate person can negate their disadvantage by declaring that "reading is bulls**t." That's because all of this stuff is, in fact, important.
Understanding This Language Is A Full-Time Job
"So crack the code for me, dammit!" you demand. "Tell me what I'm missing!" Well, first, let me ask you a seemingly unrelated question: What is dancing? Like, why is it a thing that humans do? The answer is that dancing well is also communication, and the primary message it sends is that you are good at dancing. That's it. Likewise, the primary purpose of the secret language of fashion is to communicate to others that you speak the secret language.
If that still sounds like recursive nonsense, think of it like an inside joke. Let's say I'm a fan of the show Rick And Morty, and I hear somebody in the break room at work pause from making their sandwich to say, "I'm a pickle, Morty!" That's not a statement or even a joke -- it's intended only to communicate that they are the type of person who loves that show. If I respond, "I'm Pickle Riiiiick!" then there is, again, zero information in the actual words. To an unfamiliar listener, it's nonsense. The only thing my response is communicating is "I also speak your language," because my ability to speak that language means something important.
Well, most fashion choices -- the careful selection of brands, the fierce rejection of looks that are outdated or out of season -- are simply communicating "I know what the secret fashion rules are, and am able to adhere to them." This, incidentally, should clear up a common source of confusion among guys who'll see a girl dressed in "provocative" clothing and say "See? She wants men to get aroused by her body!" If you ask that woman, she'll say she dresses to get compliments from other women. She's not lying.