See http://people.hofstra.edu/faculty/St...f_geom/tc.html

This a great online intro to differential geometry. Very well written with
some beautiful diagrams The whole thing can be downloaded as one pdf but
the diagrams aren't as pretty and the linking isn't included.

TABLE OF CONTENTS
1. Preliminaries: Distance, Open Sets, Parametric Surfaces and Smooth
Functions
2. Smooth Manifolds and Scalar Fields
3. Tangent Vectors and the Tangent Space
4. Contravariant and Covariant Vector Fields
5. Tensor Fields
6. Riemannian Manifolds
7. Locally Minkowskian Manifolds: A Little Relativity
8. Covariant Differentiation
9. Geodesics and Local Inertial Frames
10. The Riemann Curvature Tensor
11. A Little More Relativity: Comoving Frames and Proper Time
12. The Stress Tensor and the Relativistic Stress-Energy Tensor
13. Three Basic Premises of General Relativity
14. The Einstein Field Equations and Derivation of Newton's Law
15. The Schwarzschild Metric and Event Horizons
16. White Dwarfs, Neutron Stars and Black Holes by Gregory C. Levine

Oh - at http://people.hofstra.edu/faculty/St...rld/index.html
there's links to a lot of other online math tutorials by the same people.

Never be discouraged - the math of GR is hard but doable. Einstein spent
four of the eight years from special to general relativity learning and
applying differential geometry.

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Best wishes,
Perion