The best way is to be insanely curious about what people do. The deeper you take an interest in other people, the more they will be open about what they love (very important) and what they hate about their life (even more important.)
Over time you will meet somebody that will mention “I’d pay $1000 a month if somebody would fix this for me.”
There you go. That’s what you are seeking. If you start now, this could happen before you turn 16. DO NOT be concerned if you don’t know how to fix the problem. You can hire somebody to fix the problem for $500 a month and pocket the other $500. Plus you can sell the solution to people with the same problem. No sales skills? No problem. While you were busy writing down the problem and “the pain” you were basically writing the sales copy needed. Just find ANY good salesperson and they will help you create a sales letter or “copy.” as we call it.
With that money coming in, you can find a salesperson to help you find more customers for the solution you had created. But don’t worry about the money details. If you are insanely curious about other people of all ages, you will become wealthy very soon.