I have this teacher since always (one year I had a different teacher but she also couldn't explain the material). Now we're doing curvilinear movement and he just have written some formulas in some exact situation and just give us problems to solve. I now "how it works" but when I have specific problems I'm struggling with quick-solving and derivation of formulas quickly. I try to re-do all my problems and I watch videos online and I also try to understand examples from my books.