Visit the website http://www.khanacademy.org/

Watch. Practice.

Learn almost anything for free.

With a library of over 3,000 videos covering everything from arithmetic to physics, finance, and history and 315 practice exercises, we're on a mission to help you learn what you want, when you want, at your own pace.

A free world-class education for anyone anywhere.

The Khan Academy is an organization on a mission. We're a not-for-profit with the goal of changing education for the better by providing a free world-class education to anyone anywhere.

All of the site's resources are available to anyone. It doesn't matter if you are a student, teacher, home-schooler, principal, adult returning to the classroom after 20 years, or a friendly alien just trying to get a leg up in earthly biology. The Khan Academy's materials and resources are available to you completely free of charge.