Missed an important class? Khan Academy offers free courses and walkthrough lessons on basically any topic ever! It just takes a keyword and a search button.
Apart from Kahoot, Quizziz is a great tool to test your learning on subjects through fun and interactive questions. It even has memes. You cannot get bored this time.
This is simply the perfect website for when you're having trouble picturing a scientific theory. It includes visual, and interactive practical simulations of almost every concept ever that you have to learn for your exams!
BCC Bitesize is the perfect webpage to find informative summaries on any level of detail. Saves you a whole bunch of time on trying to find the right content to study from.
Not many people actually know how good of a tool this is; you can find past papers, model answers, revision guides and walkthroughs. Personally, this is the best site ever - and good preparation for the IGCSEs/GCSEs/A Levels.