[Help] Advice to get started in Physics?

I have a huge passion for Astrophysics and related fields but my understanding of these subjects is hindered by my lack of maths. I never really studied maths due to leaving school at a young age. I am, however, determined to learn in order to gain a better understanding of physics and put my own theories to the test. My question is, what kind of maths should I be studying (I've heard something about calculus) and how best to learn, I.e. is there a pathway through different models?

All advice would be hugely appreciated.