khanacademy.org is great, but the truth is, a textbook is much better than a summary. Only the full details can make a person an expect on a subject. No short cuts. Introverts are statistically shown to do better in school because they spend more time learning. There's a point when outside help won't help because they've reached a limit to their knowledge.
Source? I am a 4.0 GPA student in college researching Aging and Cancer and I've helped D students get B's and only professors can keep up with what I've learnt.