The goal of fezda.com is to offer interactive educational content.
One of the best ways to internalize a skill is to apply it in a project that you are working on. Example projects are provided, though of course you can use these skills for your own projects.
Automatically generated practice problems allow you to test and review your skills; the same problem is often presented with different values, and their multiple choice position is scrambled so that the answers can't simply be memorized, allowing you a new challenge each time.