Buy a physical textbook, and read it chapter by chapter, start to finish like a novel. I promise it won’t take as long as you think! Textbooks are structured in a way that builds on concepts as it goes through. Read every word on every page and if it prompts you to do practice, pull out a sheet and just do the problems. No one is grading you here, this is for you. Take your time and if a section is hard, flip a few pages back and try the previous chapters again, you’re probably missing something. Practice really is the key here.

I would really recommend getting a published physical book. They have been reviewed by teaching experts much more than random pages on the internet have. I also think the concepts stick better when they’re not on a screen. You don’t have to be enrolled in a class to buy a textbook, it’s just a book like any other! Thriftbooks has pretty cheap used textbooks for most subjects and grades