Mom, dad, working in restaurants and dining halls, cooking school, television, and reading cookbooks. Good cookbooks combined with television shows like the ones on PBS can provide an excellent foundation. Websites like this one can also be great resources. Just ask, "How do I make (fill in the blank)?" and you will get answers that will be very helpful. After doing this since the sixties, I'd say to any home cook, no matter if they are a beginner or an accomplished cook, read Salt Fat Acid Heat by Samin Nosrat. I am still learning all the time!