I bought Spivak Calculus on Manifolds last time and I was really really disappointed... I opened the first chapters and I understood nothing of what he was saying.
But i need to understand multivariable calculus along with tensors and all that stuff to start study General relativity next semester...
Which book do you recommend me? (someone that contain everything (Partial) Differentiation (Multiple) Integration Curves and Surfaces in R3 Vector Calculus (Green's Theorem, Stokes' Theorem, Divergence Theorem) )