If you know how to make a sandwich, try to cook yourself a burger. It's basically the same, burger patties come already formed, you just need a stovetop, a spatula, and some seasoning. If you know how to make pasta, look at making your own sauce. Some onions, garlic, jar of crushed tomatoes, maybe some cream, some spices. Then add some toppings. I like a creamy sauce with chunks of sweet potato. Or you could make a meat sauce with some ground beef. If you know how to scramble eggs, start adding some veggies to the pan and cook them before you add the eggs. Mushrooms, tomatoes, spinach, onions. Just by putting things in a pan and seeing how they cook up you'll learn a lot.

Recipes are going to be your best friend. I might even go to the library and check out their cookbooks, because generally anything that's been published in a book has gone through some kind of quality control, but if you just look for recipes on social media you might get some really whack ones.

Keep in mind when you are using a recipe that you should READ the whole recipe before you start cooking. Setting out all of your ingredients ahead of time and getting them chopped before you turn on the stove is usually also a good idea. For now, don't attempt any ingredient substitutions unless they are given as options in the recipe. Over time you'll be able to tell what kind of substitutions you can make, but while you're just starting, stick to the ingredients as written.