You don’t need to know anything beforehand.
You can start as a beginner and improve on the way. However, if you are trying to solve a specific problem (like a project that was given to you as a student project with a specific deadline), it is very helpful to watch the lectures and try to follow your tutor’s way of thought. We do know that many universities fail miserably on that point, but, still, watching the lectures may help as is participating actively in the learning process.