After each video, there are a series of challenges that give you a chance to apply what you just learned. The great thing about these challenges are that they force you to think through a problem, and use the new skills to solve it. It's not just regurgitating facts; it requires some effort.
Rather than merely test for code correctness, Exercism uses peer review to improve general programming techniques. Users are encouraged to comment on others' solutions, and refine their own based on feedback.
It's best to have at least a basic understanding of programming before tackling the exercises on exercism.io. You also have to know how to set up your development environment, as you will be coding everything locally (versus websites that provide you an editor right in the browser).