To become an expert in science, be it in physics, mathematics, philosophy or computer science, it's not enough to read learning topics and watch educational videos. Only experience makes you an expert!
That's why you can complete quests here to gain experience, as well as test your acquired knowledge and most of all consolidate knowledge. You can then compare your solution with the standard solution attached to the quest. Even if you get difficulty solving, you can at least try to understand the attached solution.