ADVICE

hi Everyone , this might seem silly and kind of late asking these questions , BUT i need to ask two questions and i will appreciate your feedback .
1- how does khan study or learn ? i mean how can he truly learn all these subjects and at the same time have the ability to contribute it to the community ? it is like elon musk learning rocket engineering.(HOW ?)
2- what is the best method for studying chemistry ? currently i'm re-taking my general chemistry , to give you some background i used to study say two to three days before exams ( not anymore) but i didn't put a lot of emphasis on practice problems , i simply read the notes and watched videos and somewhat do examples. i once asked a classmate of mine on how he studies and he told me that he works on the practice problems all the time and when he needs to understand the concepts he simply watches khan , do you think this is a good strategy ? please bear with me if you don't understand my points , it is just that since i failed this course and college algebra i came to realize i have a bad studying strategy . AND above all how i approach my learning methods for example in college algebra i could work on the problems and do ok in quizzes and exams but when it came to three part applied application projects totally worth 50 points i failed miserably to make sense of it . example how can i take the lessons i read and practiced to solve real world applications . these are the problems i'm currently trying to improve so please any feedback will be appreciated and thank you in advance .