If you clicked on the link on "My Favourite Websites" and figured out how to use it then good. If you didn't then this is how you do it. First you choose if you want to sign in using Facebook or Google. I don't have a Facebook account so I don't know how to sign in using Facebook but I assume that it is the same as signing in with Google. When signing in with Google you have to write your password and email address and voila! You are signed in!
Once you signed in you can watch the videos on the Khan Academy website and gain Energy Points to unlock avatars. Each video earns you 750 energy points depending on how much of the video you watched. You can also earn badges for doing certain things. For example watching 1 hour of video in a single topic gets you an Awesome Listener badge. When you earn certain badges like the Hard at Work badge you also get extra energy points. There are 6 different types of badges: the meteorite badges, the Moon badges, the Earth badges, the Sun badges, the Black Hole badges and the challenge badges. Meteorite badges are the easiest badges and the Black Hole badges are the hardest as they don't tell you what to do to earn them.
You can set yourself goals to achieve. You can see graphs that shows your activity, your focus, your skill progress and your progress over time. You can create computer programs. There is also an Exercise Dashboard where you can attain mastery. At the moment I have 129,871 Energy Points, I have watched 109 out of the 4149 videos, I have 35 out of the 414 stars and my avatar is Old Spice Man. My favourite topics are Science and Humanities.
Summary: I think Khan Academy is a fantastic, brilliant, informative and educational website. I give the website a 10/10.