This article largely a condensation of the material in Stephanis text thru § 1.4 and chapter 3 of Will in which I have two goals: 1) to get a better understanding of GR about which I have doubts that I've expressed elsewhere and 2) as a proofing of math ML in wikimedia.
¹ Hans Stephani. General Relativity.
² Clifford M. Will. Theory and Experiment in graviational physics.