Dive into an advanced lecture on general relativity, the first in a series from the Summer School on Gravitational Wave Astronomy. Explore the classical theory of gravitation, examining how mass and energy affect spacetime. Delve into key concepts such as the Ricci tensor, energy-momentum tensor, and Einstein equations. Investigate vacuum solutions and the behavior of test bodies in curved spacetime. Study the action of massive particles, geodesic equations, and the derivation of conserved quantities. Gain insights into black holes through Townsend's review and understand the connection to Newton's law. This comprehensive lecture, delivered by Sudipta Sarkar from IIT Gandhinagar, provides a solid foundation for graduate students and researchers in gravitational physics and related fields.