Download or get a textbook and read it yourself + find some lectures on YouTube with a high rank that you also feel you are getting something from. This is and always has been the best way to learn most subjects.
I agree that you can find resources else where but these courses have already a structure, have tests and deadlines… that makes you study! At least for me, a good structure is essential.
This is also how I do it but I would also like some sort of computer based tools to help learn.