  Einstein's theory of general relativity (GR) provides the best available
description of gravity. The recent detection of gravitational waves and the
first picture of a black hole have provided spectacular confirmations of GR, as
well as arousing substantial interest in topics related to gravitation.
However, to understand present and future discoveries, it is convenient to look
to the past, to the classical tests of GR, namely, the deflection of light by
the Sun, the perihelion precession of Mercury, and the gravitational redshift
of light. The objective of this work is to offer a non-technical introduction
to the classical tests of GR. In this first part of the work, some basic
concepts of relativity are introduced and the principle of equivalence is
analysed. The second part of the article examines the classical tests.
