Everyone says to read book "xyz", but I have never found books to helpful for several reasons.
- You can't ask a book a deep question to do with understanding.
- No book is perfect.
- I can't afford them.
- I have ADHD (although I have no difficulty sitting and thinking about math for hours because it really interests me).
- This might be different with areas of math I'm not used to, but I've always ended up learning things in the past by finding a missing piece in my understanding at which point I can derive most of everything I need, and end up skipping chapters of the book altogether.
Furthermore, I am not connected to anyone I can ask questions to, although I wish I was. Whenever I meet a mathematician, I try to do everything to make the best of the situation. I have tried using Math Stack Exchange, but it just isn't enough to fully teach yourself a subject (and additionally, I don't always feel safe asking questions here). You can visit my profile to see the kinds of questions I've been asking.
I love math. However, after going through all the regular calculus stuff, as well as multivariable and vector calculus as well as a conceptual understanding of linear algebra, I'm pretty much stuck. I've been putting more time than ever into learning math of a wide variety with almost no results.
What I do have is the internet.
Best Answer
What has worked for me is instead of searching for a "$xyz$" textbook, search for an online free class with an available syllabus. Preferably a class where you have lectures recorded, exercise lists available and a textbook which can be accessed online via a pdf file. This way you won't be intimidated by the volume of the textbook and things that you need to study will already be pinpointed and highlighted by a professor. I know that MIT and Harvard have a nice open course wares.
Good luck !