You get sequential material, too, so you can work through one lesson at a time in order until you've learned what you need to know.
Khan Academy focuses on learning materials for students in kindergarten through early college. That doesn't mean other people can't use it or find immense value in it. However, when you look at the available courses, you will notice that many closely map to the US education system. So, for example, there are courses under the heading High School Physics. Khan Academy is especially adept at teaching math, science, computing, economics, history, and personal finance, among a few other subjects. You get sequential material, too, so you can work through one lesson at a time in order until you've learned what you need to know.