It really depends on what you are trying to achieve and on your learning process. If you are studying for A levels, you could try to find more specific resources online so that the guidance is more appropriate. However, if you still can’t fully grasp a concept after you use those resources you should consider watching videos regarding that topic on khan academy. I think they really do explain things well.
Ultimately, try to identify what learning approach is better for you. For example, if you learn things quicker by watching a video and hearing somebody talking about what you should learn, then the best learning approach would be visual. On the other hand, if you find yourself learning quicker by reading stuff from a book, just get the books regarding the topics/ subjects you need to study. In general, if you can’t understand something, try to look up multiple resources that explain that specific concept until you fully grasp it.