It started with watching my grandma. Her cooking is a bit more uhh.. generic I guess. She'd always cook stuff to make sure I liked it, whereas my parents would cook stuff they liked and I either learned to like it their way or go hungry.
Then in school I ended up taking the couple cooking classes that the school offered.
After getting the basic knowledge of stuff you just kinda figure out that cooking is 99% paying attention. If you just follow recipes and such everything comes out really nice. Alternatively don't get discouraged if you experiment by making something and it doesn't turn out right.
Ya. You don't really need any classes.. Unless you're looking to make something unique purely from scratch. Then you may need to know more complex things like knowing how to find a specific taste you're looking for, but ain't no one got time fo' dat!@