Ask HN: How do I learn? Help, I'm having anxiety about this

I always wonder how to approach the study of a subject, such as Mathematics, for example. I want to self-learn it, but I'm unsure of how to begin. Which books should I read, and where can I find them? With hundreds of books available, I aim to learn in a sequential and progressive manner, starting from arithmetic and progressing to the graduate level. Similarly, for biology, I am uncertain about where to start and how to proceed. What books should I read to cover the subject comprehensively from beginning to end?

This thing is causing anxiety within me because subjects are long and too many things to read but I'm not even getting started.