>>12336163I highly recommend studying classical mechanics. Lagrangian formulation is very essential to all advanced level physics like GR and QFT.
I think most GR courses go like this: special relativity and relativistic mechanics -> basic differential geometry (tensor, manifold) -> Riemannian geometry (metric, geodesic, curvature) -> Einstein field equation from Hilbert-Einstein action -> special solutions like Schwarzschild metric -> advanced topics (blackhole, cosmology, singularity, quantum effect in the curved spacetime etc)
So GR can be summarized expressing physical meaning on the curvature of spacetime by metric tensor of manifold from (pseudo) Riemannian geometry IMO.
Many people recommend Carroll, MTW, Weinberg, Hartle as its textbook, but it sucks I suppose. Zee's Einstein gravity in the nutshell or Gron & Hervik's book is good introduction.
