With all due respect, I have to disagree, I would not start at sauces or think knowing how to make a sauce means you can cook anything. Knowing how to make a hollandaise sauce does not help me trying to Roast Chicken. Knowing how to cook is knowing more than just mask things with flavour. Sauces are a compliment, they add to the dish, they are not the main dish. A red wine sauce on a steak adds to the steak, you can eat a perfectly good steak without sauce. A nice piece of wagyu is best eaten with no sauce.
Cook some steamed dumplings, you don’t need any sauce. Or an Apple Pie or Miso Soup, no sauce. What sauce do you make to help you make dumplings if you don’t know how to make dumplings?
I would say knowing how to make a sauce will be like 5% of learning how to cook, you are going to live a very narrow set of dishes if everything depends on the sauce.
Learn how to cook first, then learn how to take it to the next level with good sauces. I can’t remember the last time I actually made a sauce, may be 5 months ago when I made it for Korean fried chicken. Or may be the tonkatsu one for my home made chicken nuggets. But the key to both really is know how to make the fried chicken first, know how hot the oil needs to be, know double fry technique, know what to season the flour with. The chicken was perfectly fine without any sauce, just like KFC does but dunking it with some nice spicy sauce takes it up a notch.